690A-0999 M1 Series sm.p65

M1 Series

Service Manual

M1G and M1M Furnaces

Typical meters used to service M1 furnaces.

A. Differential Pressure Gauge

B. Volt-Ohm Meter

C. Manometer

D. Inclined Manometer

TABLE OF CONTENTS

1. INTRODUCTION

Model Identification Code ........................................ 4

Serial Number Identification .................................... 4

Clearances and HUD Requirements ....................... 5

Unit specifications ................................................... 5

2. CIRCULATING AIR SUPPLY

Return air requirements .......................................... 6

Blower performance data ........................................ 6

Supply air systems .................................................. 7

3. VENTING AND COMBUSTION AIR

Roofjack selection ................................................... 7

Roofjack troubleshooting......................................... 7

Application of high wind and arctic caps.................. 8

4. ELECTRICAL WIRING

Line voltage............................................................. 8

Low voltage ............................................................. 9

5. GAS SUPPLY,CONVERSION AND LIGHTING

M1G,M1M MODELS

Gas piping ............................................................. 10

Gas conversion nat to LP ...................................... 10

Gas safety nat and LP........................................... 11

Derating for high altitude ....................................... 11

Proper pilot lighting M1G only ............................... 12

Leak checking gas line .......................................... 12

6. ACCESSORIES

Relay boxes .......................................................... 13

Cooling blowers..................................................... 13

Furnace accessories for package unit add on ....... 13

Fan timer kit .......................................................... 13

All Weather Cap ................................................... 13

7. SEQUENCE OF OPERATION , COMPONENT PARTS

AND TROUBLESHOOTING, M1G

STANDING PILOT MODEL M1G

Troubleshooting flow chart M1G-056-070 ............. 15

Troubleshooting flow chart M1G-077-090 ............. 16

Sequence of operation heating.............................. 17

TROUBLESHOOTING

Power supply ........................................................ 17

Transformer .......................................................... 17

On-off switch and fan switch ................................. 17

Low voltage wiring................................................. 18

Limit controls ......................................................... 18

Combustion air relay, 077 and 90 only .................. 18

Combustion air blower, 077 and 90 only ............... 18

Pressure switch, 077 and 90 only ......................... 18

Burner assembly ................................................... 19

Gas valve .............................................................. 20

Pilot assembly, Thermocouple, and Venturi .......... 20

Fan switch............................................................. 21

Blower assembly ................................................... 21

Heat exchanger..................................................... 22

Pilot outage ........................................................... 22

Pilot Outage Chart................................................. 23

WIRING DIAGRAMS

M1G, Natural Draft, AC adaptable........................ 24

M1G, Natural Draft, AC ready .............................. 24

M1G, Forced Draft, AC adaptable ........................ 25

M1G, Forced Draft, AC ready............................... 25

8. HOT SURFACE IGNITION SYSTEM MODEL M1M

Troubleshooting flow chart .................................... 27

Sequence of operation heating.............................. 28

TROUBLESHOOTING

Power supply ........................................................ 28

Transformer .......................................................... 28

Low voltage wiring................................................. 29

Limit controls ......................................................... 29

Intergrated control board ....................................... 29

Combustion air blower .......................................... 31

Pressure switch..................................................... 32

Hot surface ignitor ................................................. 33

Burner assembly ................................................... 33

Gas valve .............................................................. 33

Blower assembly ................................................... 34

Heat exchanger..................................................... 34

WIRING DIAGRAM

M1M, All ................................................................ 35

Model Identification

Door Color

W = White

G = Gray

Cabinet Size

A = 20" x 24" x 56”

B = w/Coil Cavity, 20” x 24” x 76”

Electrical Code

A = 1PH, 60 Hz, 120 VAC

Heating Capacity

Input, BTUH (000)

Application

M = Manufactured Home

Furnace Series

Fuel, Type of Combustion

G = Gas, Direct Vent, Pilot Burner

Natural or Forced Draft

M = Gas, HSI, Forced Draft

B = Gas, Gun Burner

S = Oil, Gun Burner

M 1 G H - 056 A - BW

Comfort Model

H = Heating

A = Heating, A/C Ready

B = A/C Ready, 3 Ton

C = A/C Ready, 4 Ton

D = A/C Ready, 5 Ton

INTRODUCTION

This service manual is designed to be used in conjunction with

the installation manual provided with each furnace.

The downflow sealed combustion furnaces illustrated in this

service manual represent the very latest in high efficiency gas

furnace technology. Certain controls within the furnace

consist of highly sophisticated electronic components which

are not user serviceable. It is essential that only competent,

qualified, service personnel attempt to install, service, or

maintain this product.

This Service manual was written to assist the professional

HVAC service technician to quickly and accurately diagnose

and repair most malfunctions of this product.

This service manual covers standing pilot and hot surface

ignition gas burner models. The overall operation of both of

these models is essentially the same, with the exception of

certain controls which may be unique to each model.

This manual will deal with all subjects in a general nature (i.e.

all text will pertain to all models) unless that subject is unique

to a particular model or family, in which case it will be so

indicated.

It will be necessary for you to accurately identify the unit you

are servicing, so you may be certain of approved diagnosis

and repair. (See Unit Identification, Below)

This manual was prepared by the senior Technical Service

Department and the Communications Department.

The information contained in this manual is intended for use

by a qualified service technician who is familiar with the safety

procedures required in installation and repair and who is

equipped with the proper tools and testing instruments.

Installations and repairs made by unqualified persons can

result in hazards subjecting the unqualified person making

such repairs to the risk of injury or electrical shock which can

be serious or even fatal not only to them, but also to persons

being served by the equipment.

If you install or perform service on equipment, you must

assume responsibility for any bodily injury or property dam-

age which may result to you or others. We will not be

responsible for any injury or property damage arising from

improper installation, service, and/or service procedures.

WARNING:

Serial No. Identification

Model Series

M 1 G 9807 - 05432

Production

Year/Month

Production Code

Table 1. M1 Furnace Specifications

NOTICE TO INSTALLER

Installer is advised to follow carefully all instructions and

warnings in this manual to insure maximum performance,

safety, and operating efficiency of these appliances. Improper

installation may create hazardous conditions, and will void the

appliance warranty.

1. SPECIFICATIONS

GENERAL DESCRIPTION

M1 Series gas and oil furnaces are listed direct vent (sealed

combustion), downflow heating appliances for manufactured

(mobile) homes, recreational vehicles, and for use in residen-

tial/modular/commercial construction. The furnace must be

located so that venting can be properly achieved.

“A” cabinet models may be installed with Optional Coil Cabi-

net Model #911969 for air conditioning.

“B” cabinet models are factory equipped with a built-in coil cavity.

Multi-speed blower assemblies (See Accessories) have been

certified for field installation in M1 Series furnaces. An air

conditioner can be easily field installed with M1GH Series

furnaces if used in conjunction with certified 2-wire relay box,

p/n 903092A or 4/5 wire relay box 902898A.

INSTALLATION STANDARDS

Installer shall be familiar with and comply with all codes and

regulations applicable to the installation of these heating

appliances and related equipment. In lieu of local codes, the

installation shall be in accordance with the current provisions

of one or more of the following standards.

Electrical Supply - 120 Volts, 60 Hz, 1 Ph. Thermostat Circuit - 24 Volts, 60Hz, 30 VAC

Fuse or Breaker - 15 Amps. Norm. Anticipator Setting - 0.4

Temperature Rise - 45° to 75°F Manifold Pressure - Natural Gas - 3.5” w.c. LP Gas - 10” w.c.

High Altitude - See Table 7. *Nominal blower capacity only – relay must be field added.

For Canadian High Altitude (2,000'-4,500'),reduce the gas manifold pressure to 3.0" w.c. for natural gas and to 8" w.c. for LP gas.

Furnace Input Output Orifice No E.S.P. Pilot Ignitor Comb. Motor A/C Ready

Model No MBtu/h MBtu/h Nat. LP In WC Burner Direct Blower Hp Tons

M1GH 056 56 45 29 45 0.2 x 1/8 2*

M1GB 056 56 45 29 45 0.3 x 1/3 3

M1GC 056 56 45 29 45 0.3 x 1/2 4

M1GD 056 56 45 29 45 0.3 x 3/4 5

M1GH 070 70 57 24 42 0.3 x 1/5 2½*

M1GB 070 70 57 24 42 0.3 x 1/3 3

M1GC 070 70 57 24 42 0.3 x 1/2 4

M1GD 070 70 57 24 42 0.3 x 3/4 5

M1GH 077 77 60 21 40 0.3 x x 1/4 3*

M1GB 077 77 60 21 40 0.3 x x 1/4 3

M1GC 077 77 60 21 40 0.3 x x 1/2 4

M1GD 077 77 60 21 40 0.3 x x 3/4 5

M1GH 090 90 70 17 36 0.3 x x 1/4 3*

M1GB 090 90 70 17 36 0.3 x x 1/4 3

M1GC 090 90 70 17 36 0.3 x x 1/2 4

M1GD 090 90 70 17 36 0.3 x x 3/4 5

M1MA 056 56 46 29 45 0.2 x x 1/8 2

M1MB 056 56 46 29 45 0.3 x x 1/3 3

M1MC 056 56 46 29 45 0.3 x x 1/2 4

M1MD 056 56 46 29 45 0.3 x x 3/4 5

M1MA 070 70 57 24 42 0.3 x x 1/5 2½

M1MB 070 70 57 24 42 0.3 x x 1/3 3

M1MC 070 70 57 24 42 0.3 x x 1/2 4

M1MD 070 70 57 24 42 0.3 x x 3/4 5

M1MB 077 77 62 21 40 0.3 x x 1/4 3

M1MC 077 77 62 21 40 0.3 x x 1/2 4

M1MD 077 77 62 21 40 0.3 x x 3/4 5

M1MB 090 90 72 17 36 0.3 x x 1/4 3

M1MC 090 90 72 17 36 0.3 x x 1/2 4

M1MD 090 90 72 17 36 0.3 x x 3/4 5

a. Federal Manufactured Home Constructions & Safety

Standard (H.U.D. Title 24, Part 3280.707[a][2])

b. American National Standard (ANSI-119.2/NFPA-501C)

for all recreational vehicle installations.

c. American National Standard (ANSI-Z223.1/NFPA-54)

and/or CAN/CGA B149 for all gas-fired furnace models.

d. American National Standard (ANSI-Z95.1/NFPA-31) and/

or CSA B139 for all oil-fired furnace models.

e. American National Standard (ANSI-C1/NFPA-70) and/or

CSA 22.1 Canadian Electric Code Part 1 for all electrical

field wiring.

f. Units have been investigated under standards UL 307A

& B, ANZI 21.47a — CAN/2.3a - 1995, and CSA B140.10.

2. CIRCULATING AIR SUPPLY

RETURN AIR PROVISIONS

U.S.A. home manufacturers shall comply with all of the

following conditions to have acceptable return air systems for

closet installed forced air heating appliances:

a. Regardless of the location, the return air opening into the

closet shall not be less than specified in the appliance’s

listing.

b. Means shall be provided to prevent inadvertent closure

by a flat object placed over the return air opening when it

is located in the floor of the closet (versus the vertical front

or side wall).

c. The cross-sectional area of the return duct system lead-

ing into the closet, when located in the floor or ceiling shall

not be less than 235 square inches (or 390 square inches

for 5 ton ready M1 Furnaces).

d. The total free area of openings in the floor or ceiling

registers serving the return air duct system must be at

least 352 sq. in. At least one register should be located

where it is not likely to be covered by carpeting, boxes and

other objects.

e. Materials located in the return duct system must have a

flame spread classification of 200 or less. This includes a

closet door if the furnace is in a closet.

f. Noncombustible pans having 1" upturned flanges are

located beneath openings in a floor duct system.

Table 2. Blower Performance Data

ESP

(In. W.C.)

Low Med-Lo Med-Hi High Low Med-Lo Med-Hi High

1/8 HP 1 024 0.1 820 730

9 X 7.5 0.2 790 680

0.3 720 610

056 - H, A 0.4 650 550

UNITS 0.5 560 450

0.6 430 330

1/5 HP 1 030 0.1 950 850

9 X 7.5 0.2 910 810

066-A 0.3 850 730

070 - H,A 0.4 780 670

UNITS 0.5 680 580

0.6 570 480

1/4 HP 1 036 0.1 1210 1140

10 x 8 0.2 1190 1110

077 - H, B 0.3 1140 1050

090 - H, B 0.4 1090 990

086-B 0.5 1030 930

UNITS 0.6 970 870

1/3 HP 2 036 0.1 1020 1350 960 1210

10 x 8 0.2 1000 1330 940 1170

056 - B 0.3 970 1260 890 1110

070 - B 0.4 940 1210 850 1050

UNITS 0.5 890 1130 790 980

0.6 840 1060 730 900

1/2 HP 4 047 0.1 890 1070 1270 1480 880 1050 1220 1340

11 X 8 0.2 880 1060 1260 1460 870 1040 1210 1330

0.3 860 1020 1220 1400 850 1000 1160 1270

C UNITS 0.4 840 1000 1180 1350 820 980 1110 1210

0.5 810 960 1120 1280 800 940 1070 1160

0.6 760 920 1080 1220 750 890 1010 1090

3/4 HP 4 054

10 x 8 0.2 900 1110 1450 1850 870 1070 1420 1700

4 POLE 0.3 860 1080 1410 1810 840 1050 1380 1650

0.4 830 1040 1370 1760 820 1030 1350 1630

D UNITS 0.5 790 1020 1340 1730 780 1010 1320 1590

0.6 770 990 1320 1700 760 980 1290 1550

HP, Wheel,

Poles, Units

Coil

Size

WITHOUT COIL WITH COIL

Speed

g. Wiring materials located in the return duct system shall

conform to Articles 300-22 of the National Electrical

Code (ANSI C1/NFPA-70).

h. Gas piping is not run in or through the return duct system.

i. Test the negative pressure in the closet with the air-

circulating fan operating at high speed and the closet

closed. The negative pressure is to be no more negative

than minus 0.05 inch water column.

j. For floor return systems, the manufactured home manu-

facturer shall affix a prominent marking on or near the

appliance where it can be easily read when the closet

door is open. The marking shall read:

k. Air conditioning systems may require more duct, register

and open louver area to obtain necessary airflow. Use

NORDYNE’s certiduct program to determine proper

duct size for A/C.

Air Distribution Systems

For proper air distribution, the supply duct system must be

designed so that the static pressure measured external to the

furnace does not exceed the listed static pressure rating

shown on the furnace rating plate.

Before installing an air conditioner system, consult home

manufacturer for duct system maximum capacity. Location,

size, and number of registers should be selected on the basis

of best air distribution and floor plan of the home.

Table 3. Roof Jack Assemblies

CAUTION:

HAZARD OF ASPHYXIATION: Do not cover or

restrict return air opening.

3. VENTING AND COMBUSTION AIR

ROOF JACK SELECTION

Note: Install only Roof Jack Assemblies listed in Table 3 on

this heating appliance.

a. Determine depth of ceiling cavity from center of roof

opening to center of ceiling opening. (See Dimension “A”

in Figure 1).

b. Determine ceiling height and subtract height of furnace.

(See Dimension “B” in Figure 1).

c. Add dimensions A + B (and X from Table 3 and Figure 2

if slant deck flashing is used). The total length of (A + B +

X) must be within the minimum and maximum range of

one of the Roof Jacks listed in Table 3.

ROOF JACK TROUBLE SHOOTING

The roof jack assembly is a telescoping type assembly (see

selection) that is made up of a pipe within a pipe construction.

The inner pipe (5”) is for the flue gases to exit the home. The

outer pipe (8”) is using the space in-between the 5” and 8” pipe

for combustion air. If the furnace is smothering itself out, after

a short time, on natural draft models, or pressure switch does

not make contact on M1M model, slide up air inlet a few inches

and check for debris in pipe. Clean out and check complete

flue assembly for blockage. On new homes make sure no

building materials fell in the top (air inlet or exhaust). Also

remove top and make sure no seams have opened up on roof-

jack assembly. On the M1G furnace (natural draft model) the

air inlet limit tripping is caused from a unbalanced draft, which

means the air inlet becomes a better flue than the flue itself.

Check-out Procedure:

 Is furnace filter clean?

 If furnace is installed in closet, what is the louver open area?

The installation instructions state the minimum open area

required is 235 sq. in., or 390 sq. in. for 5 ton.

 Inspect roof-jack for internal blockage.

 Inspect inside of upper combustion air box for debris.

 With burner removed, reach inside lower air box into com-

bustion air chute to check for debris (insulation, roofing

material, drywall, etc.) and look in the bottom of the heat

exchanger for debris.

SSAW

47 - 2

AW= ALL WEATHER

FLASHING

PITCH/12" RISE

0=FLAT

2=2.5/12

4=4/12

MIN. ADJ.

LENGTH

FLAT FLASHING

SLANT FLASHING

TYPE:

BLANK=NON-TRANSIT

T= TRANSIT MODE

MAX. ADJ.

LENGTH

FLUE STEEL TYPE

A= ALUMINIZED

S=STAINLESS

Approx. Length

Model Number Below Flashing

(F,S)AW(T)1523-(0,2,4)(A,S) 15" - 23"

(F,S)AW(T)2135-(0,2,4)(A,S) 21" - 35"

(F,S)AW(T)2747-(0,2,4)(A,S) 27" - 47"

(F,S)AW(T)3563-(0,2,4)(A,S) 35" - 63"

(F,S)AW(T)5195-(0,2,4)(A,S) 51" - 95"

 Is gas orifice the proper size for the gas in use?

 Check manifold gas pressure at low fire (14 seconds

nominal) before it steps to normal high fire.

 The compression fitting on the pilot tube must be tight.

 Is the burner aligned perpendicular to the burner mounting

plate?

APPLICATION OF ALL WEATHER CAPS

In most cases, when a pilot is blown out during windy condi-

tions, an all weather cap will take care of this problem.

Extension(s) will also help (see Pilot Outage). See Accessory

Chart for part numbers.

All weather caps are used in areas of extreme cold (10° or

lower) for long periods of time. This causes ice to form and

block combustion air. Replace the standard crown with the

optional all weather cap. Follow instructions with the new all

weather cap. See Accessories section for part number.

a. If the roof jack crown is covered or blocked with snow, the

furnace will not operate properly. If the home is located in

regions where snow accumulation exceeds 7” (HUD

snowload zones) use an external roof jack extension p/n

901937.

b. M1 furnaces may be used with roof jacks as tall as 170”

(except M1M 056 models, which are limited to 120”).

Internal roof jack extensions (p/n 901935 - 10”, p/n 903107

- 18”) can be used to increase roof jack height. All connec-

tions inside the home must be made below the ceiling.

ELECTRICAL WIRING

Line Voltage Wiring (See Figure 15)

The line voltage (115 volt) to the furnace must be supplied

from a dedicated circuit containing the correct fuse or circuit

breaker for the furnace. See Table 5. An electrical switch

should be readily accessible from and within sight of the

furnace. All line voltage connections must be made within the

junction box located within the furnace.

The furnace cabinet must have an uninterrupted, unbroken

ground to minimize injury should an electrical fault condition

occur. The controls used in this furnace also require an earth

ground to cooperate properly. Acceptable methods for ground-

ing are electrical wire or conduit approved for electrical ground

service. Do not use gas piping as an electrical ground.

NOTE: Proper line voltage polarity must be maintained in

order for the control system to operate correctly. Verify

that the incoming neutral line is connected to the white

wire and the incoming "hot" line is connected to the black

wire in the furnace junction box. This furnace will not

operate unless polarity and ground are properly con-

nected. (See Figure 16).

Never use gas lines as ground.

To determine polarity, the incoming power supply should be

checked. The "Hot" lead will read 115V to ground. The

"neutral" should read 0V to ground.

Figure 2.

Figure 3.

Figure 1. Roof Jack Assemblies

Roof Jack

Flat Roof

Ceiling Cavity

Ceiling

Flue Pipe

Combustion

Air Pipe

Flashing

This joint

may be

above ceiling

"A"

"B"

56" or 76"

Furnace

5/12 ROOF SLOPE

SLANT DECK

/12

ROOF JACK WITH

FLASHING

/12 SLANT

ROOF JACK

SLANT DECK

FLASHING

PITCHED

ROOF

CEILING

CEILING CAVITY

ROOF OPENING

CEILING OPENING

"X" (SEE TABLE 1)

Supply Voltage

Supply voltage to the furnace should be nominal 115 volts. It

must be between 103 volts and 127 volts. Supply voltage to the

furnace should be checked with furnace in operation and blower

running. Voltage readings outside the specified range can be

expected to cause operating problems. Their cause MUST be

investigated and corrected.

CONNECT THERMOSTAT WIRES

a. Insert 24 volt wires through the plastic grommet just

above the control panel.

b. Connect the thermostat wires to the furnace low voltage

pigtails (see Figure 5).

c. Connect low-voltage circuit to the wall thermostat.

d. A hole may be made in the furnace cabinet to ease

thermostat wiring. Make sure that the wiring is protected

from the sharp edge of the added hole.

NOTE: The thermostat should be installed 4 to 5 feet above

the floor on an inside wall which is relatively free from direct

sources of heat or cold drafts. The nominal anticipator setting

is 0.4. (Refer to the thermostat literature for additional infor-

mation.)

Five-conductor thermostat wire is recommended for 24 volt

low-voltage circuit (2-wire is required for furnace only; 5-wire

for heating and optional cooling systems).

Once the furnace is installed check the thermostat anticipator

against the nominal setting of 0.4:

1. Connect the milliamp meter in series with the “W” circuit.

2. Energize a call for heat.

3. Read the value of the milliamps.

4. Adjust the heat anticipator of the thermostat to the value

read on the milliamp meter.

If the heat anticipator is set too high the furnace may delay in

coming on.

If the heat anticipator is set too low the furnace may cycle

frequently and not provide the desired comfort level.

Figure 6. Line Voltage Field Wiring

T’STAT

Wire Gauge

2-Wire 5-Wire

(Heating) (Heating/Cooling)

24 55 25

22 90 45

20 140 70

18 225 110

Recommended T’STAT Wire

Len

(

Unit to T’STAT

)

Table 4. Thermostat Wire Gauge

Figure 5. Control Panel (All Models)

To Combustion

Blower or

Flame Roll-Out

Switch

Thermostat Wires

Blower

Plug

On-Off

Switch

On-Auto

Switch

(Heating

Models Only)

To Gas Valve

or Burner

Power

Entry

Furnace

Control Box

Figure 4. Thermostat Wiring A/C Ready Models

Red

White

Green

Yellow

Red

White

Green

Grey

To Cooling Unit

Thermostat

M1G A/C

Ready Furnace

Field Supplied

Disconnect Within

Sight of Furnace

Field Supplied

Panel Connector

Field Supplied

Fused Service

Panel

Black (Hot)

White (Neutral)

Green or Bare (Ground)

Black

White

Black

White

Black

White

Field Line Voltage

Wiring

Factory Line

Voltage Wiring

Ground

f. It is not necessary to convert the pilot orifice.

g. For Honeywell gas valves with the regulator converter

(Figure 8), check for the letters NAT or LP on the pressure

regulator cap. Unscrew the cap, invert it, replace, and

tighten until snug.

h. For the Robertshaw gas valve with the regulator con-

verter (Figure 9), remove the black cover and unscrew

the converter located on top of the gas valve. Invert the

converter. (For “LP” the red ring will be located at the

bottom and the “LP” stamping on the converter will appear

right side up.) Then screw converter back into the regu-

lator, hand tight plus 1/8 turn, and replace the black cover

onto the converter top to protect the threads.

i. Reassemble the burner assembly into the furnace.

j. Reconnect the gas piping and electrical wires to the gas

valve.

k. Open the manual shut-off valve and follow the FURNACE

START-UP procedure as outlined previously in this manual

to put the furnace into operation.

NOTE: The pilot flame is adjustable by turning the adjustment

screw located on the gas valve with a small screwdriver. (See

Figure 10)

5. GAS SUPPLY, CONVERSION, AND

LIGHTING – M1G AND M1M MODELS

GAS PIPING

Sizing and installation of fuel lines must be in accordance with

federal, state and local regulations. All piping shall be black

iron pipe, or equivalently sized steel tubing. Internally tinned

copper tubing may be used for gas supply systems.

Fuel line installations other than typical installations shown in

Figure 7 must comply with the fuel piping provisions stated in

the Federal Manufactured Home Standard (H.U.D. TITLE 24,

PART 280) and the National Fuel Gas Code (ANSI-Z223.1/

NFPA-54).

a. Optional fuel inlet lines are available for all gas furnace

models to permit the addition of a 1/2" F.P.T. shut-off

valve above the floor.

NOTE: Shut-off valve must be designed and listed for use

with liquid petroleum (LP gas).

The gas supply to your home will either be Natural Gas or LP

(bottle gas). Your furnace is factory equipped to operate on

Natural Gas. If your gas supply is LP, you must convert the

furnace. The necessary instructions for the gas conversion are

found on the lighting instruction label attached to the furnace in

Section 16, Service Guide.

For natural gas operation, the furnace is designed for 7" W.C.

inlet pressure. Pressure is reduced to 3-1/2" W.C. by the

pressure regulator in the gas valve. The maximum inlet

pressure for the valve is 13” W.C.

For L.P. gas, pressure to the gas valve must be more than 11"

W.C. but not more than 13" W.C. Pressure is reduced to 10"

W.C. by the pressure regulator in the gas valve.

GAS CONVERSION

This gas fired heating appliance was shipped from the factory

for use with natural gas. However, the appliance can be

converted for use with LP gas. Use the following procedure

for gas conversion of the burner.

ATMOSPHERIC AND DIRECT IGNITION FURNACES

a. Follow the instructions to “Turn Off Gas to the Appliance.”

b. Disconnect the gas pipe union and the electrical wires

connected to the gas valve.

c. Remove the pilot tube and thermocouple from the gas

valve (M1G* only).

d. To remove the gas valve assembly, remove screw(s)

from gas valve bracket. Gas valve and spud may be

removed. Orifice is located at the end of the spud

(M1G*,M1M*).

e. Replace the main orifice with the L.P. gas orifice supplied

in the envelope located by the gas valve. Check to insure

the orifice size matches the nameplate. NOTE: For eleva-

tions over 2,000 feet, use Table 7 to determine orifice size.

To Gas

Supply

Floor

Control

Panel

On-Off-Fan

Switch

Alt. Fuel

Line Entry

Floor Cavity

Figure 7. Typical Gas Piping

CAUTION:

The furnace must be converted by a qualified

technician. Improper conversion can cause

unsafe operation, explosion, fire and/or

asphyxiation.

LIGHTING AND FURNACE SHUTDOWN

GENERAL-ALL MODELS

Read the safety information on the front page of these

installation instructions before lighting furnace. DO NOT

ATTEMPT TO LIGHT FURNACE IF YOU SMELL GAS.

SAFETY INFORMATION

FOR YOUR SAFETY READ BEFORE LIGHTING.

a. The first lighting of the furnace after any home setup

must be performed by a qualified service technician.

b. If this appliance has a pilot that must be lit by hand, follow

these instructions exactly.

c. BEFORE LIGHTING smell all around the furnace for gas.

Be sure to smell next to the floor because some gas is

heavier than air and will settle on the floor.

d. WHAT TO DO IF YOU SMELL GAS: Do not try to light

any appliance. Do not touch any electric switch and do

not use any phone in your building. Immediately call your

gas supplier from a neighbor’s phone. Follow the gas

supplier’s instructions. If you cannot reach your gas

supplier, call the fire department.

e. Use only your hand to push in the gas control lever. Never

use tools. If the lever will not push in by hand, don’t try to

repair it. Call a qualified service technician. Force or

attempted repair may result in a fire or explosion.

f. Do not use this furnace if any part has been under water.

Immediately call a qualified service technician to inspect

the furnace and to replace any part of the gas valve or

control system which has been under water.

Reference Sources: ANSI Z233.1 & NFPA 54, National Fuel Gas Code.

For Canadian high altitude (2,000 - 4,500'), reduce gas manifold pressure to 3.0” W.C. for natural gas and 9” W.C. for LP gas.

NOTE: Do not attempt to change the size of an orifice by drilling it out. To do so will void the manufacturer’s warranty.

Table 7. High Altitude Derate

Figure 8. Convertible Pressure Regulator Cap

PRESSURE

REGULATOR

CAP

M11678

OTHER SIDE

OF CAP

Honeywell

Valve

Figure 9. Convertible Pressure Regulator

Robertshaw

Valve

FURNACE ORIFICE SIZE AND ALTITUDE - FEET

MODEL OUTPUT CAPACITY SEA LEVEL 2000 3000 4000 5000 6000 7000 8000 9000 10000

ORIFICE SIZE - NAT. GAS 29 293030303031313132

M1M/G 056 ORIFICE SIZE - LP 45 46 47 47 47 48 48 49 49 50

OUTPUT- MBTUH 45.4 41.8 40.1 38.5 37.0 35.5 34.1 32.7 31.4 30.2

ORIFICE SIZE - NAT. GAS 24 252627272828292930

M1M/G 070 ORIFICE SIZE - LP 42 42 43 43 43 44 44 45 46 47

OUTPUT- MBTUH 56.7 52.3 50.2 48.2 46.2 44.4 42.6 40.9 39.3 37.7

ORIFICE SIZE - NAT. GAS 21 232324252627282829

M1M 077 ORIFICE SIZE - LP 40 41 42 42 42 43 43 44 44 45

OUTPUT- MBTUH 61.7 56.9 54.6 52.4 50.3 48.3 46.4 44.5 42.7 41.0

ORIFICE SIZE - NAT. GAS 21 232324252627282829

M1G 077 ORIFICE SIZE - LP 40 41 42 42 42 43 43 44 44 45

OUTPUT- MBTUH 59.9 55.2 53.0 50.9 48.9 46.9 45.0 43.2 41.5 39.8

ORIFICE SIZE - NAT. GAS 17 181919202122232426

M1M 090 ORIFICE SIZE - LP 36 37 38 38 39 40 41 41 42 43

OUTPUT- MBTUH 71.7 66.1 63.5 60.9 58.5 56.1 53.9 51.7 49.7 47.7

ORIFICE SIZE - NAT. GAS 17 181919202122232426

M1G 090 ORIFICE SIZE - LP 36 37 38 38 39 40 41 41 42 43

OUTPUT- MBTUH 69.7 64.2 61.7 59.2 56.8 54.6 52.4 50.3 48.3 46.3

LIGHTING INSTRUCTIONS FOR STANDING

PILOT MODELS

a. Stop! Read the safety information.

b. Set the thermostat to the lowest setting.

c. Turn off all electric power to the appliance.

d. Push in the gas control lever slightly and move left to

“OFF.” DO NOT FORCE.

e. Wait ten (10) minutes to clear out any gas. If you smell

gas, STOP! Follow step “d” in the SAFETY INFORMA-

TION. If you don’t smell gas, go to the next step.

f. Find pilot - follow metal tube (pilot tube) from gas control

valve. Open hinged fire observation door. The pilot is

found at the end of the pilot tube, just left of the pilot shield.

g. Slightly depress the gas control lever and move it right to

the “ON” position and release; then move it to the “PILOT”

position.

h. Move the control lever to “SET” and hold. Immediately

light the pilot with a match. If this furnace is equipped with

a Piezo Ignitor, activate spark lever/button several times

until flame is visible through observation door. Continue

to hold the control lever for about one (1) minute after the

pilot is lit. Release the lever and it will spring back to the

“PILOT” position. Pilot should remain lit. If it goes out,

repeat steps “d” through “h” above. If the lever does not

spring back when released, stop and immediately call

your service technician or gas supplier. If the pilot will not

stay lit after several tries, move the gas control lever to

“OFF” and call your service technician or gas supplier.

i. Move the gas control lever left to “ON”.

j. Turn on all electric power to the furnace. Set the thermo-

stat to “Heat” and/or the desired temperature setting. Set

the On-Off-Fan switch to “ON”.

k. Replace the furnace door.

In the event of any flashback or explosion, immediately shut

off the furnace and call your service technician.

TO TURN OFF GAS TO APPLIANCE:

a. Set the thermostat to the lowest setting.

b. Turn off all electric power to the appliance at breaker or

fuse box, before servicing.

c. Remove the furnace door.

d. Push in the gas control lever slightly and move to the left

to “OFF.” DO NOT FORCE.

e. Replace the furnace door.

Leak Check

After the gas piping to the furnace is complete, all connections

must be tested for gas leaks. To check for leaks use only a

soap and water solution or other approved method.

NOTE: When pressure testing gas supply lines at pres-

sures greater than 1/2 psig (14 in. water column), the

furnace must be disconnected from the gas supply pip-

ing system to prevent damage to the gas control valve.

If the test pressure is less than or equal to 1/2 psig (14 in.

water column), the furnace must be isolated from the gas

supply line by closing off the main shut-off valve.

CAUTION:!

Do not use matches, lighters, candles or other

sources of open flame to check for gas leaks.

Figure 11. Lighting Furnace

Pilot

Bracket

Gas Control Lever

Pilot Adjustment

Figure 10. Standing Pilot Valve

6. ACCESSORIES

Relay Boxes

Only the M1GH requires a relay box. All other M1G and M1M

furnaces are AC ready. The M1GH series furnaces are

certified to be used with either a 4 wire relay box (p/n 902898A)

or a 2 wire relay box (p/n 903092A). Follow the instructions

included with the relay box for proper installation.

Cooling Blowers

If you are installing an AC system which exceeds the maxi-

mum AC capacity of your system, a larger blower will have to

be installed. A blower assembly may also need to be installed

for high static pressure applications or crossover systems.

Refer to “Blower Data” for further information.

A/C Capacity

Blower Wheel Motor-Hp Ton

903412 10 x 8 1/3 2, 2½ & 3

903413 11 x 8 1/2 2, 2½, 3 & 4

903414 10 x 8 3/4 2, 2½, 3, 4 & 5

Part No.

Blower / Motor Assembly

Table 8. Field Installation Blower Assemblies

Fan Timer Kit

The M1G furnace uses a temperature activated switch type

fan control (The M1M uses a time delayed control, so this

information does not apply). A fan timer kit may need to be

installed with this type of switch if the following conditions

exist:

1. Very cold outside air temperatures being drawn in through

the VentilAire system.

2. Night time thermostat set back to a very low temperature.

3. System is left off for extended periods of time.

The fan may be cycling during a normal call for heat. For gas

models, make sure the gas valve is reaching high fire. If there

are no problems with the firing rate, install a Nordyne fan timer

kit, part number 903490. See instructions with kit for installa-

tion. Since many factors outside our control may contribute

to blower short cycling, Nordyne does not consider this to be

a warranty issue.

Optional Add-On Air Conditioning – Packaged Units

Necessary when the Furnace is Used with Some Central Air

Conditioners –

If an air conditioner is installed that does not

use the furnace blower for air distribution and that operates

independently of the furnace, the thermostat system must

have an interlock to prevent the furnace and air conditioner

from operating at the same time. This interlock system usually

contains either a “Heat-Cool” switch which must be turned to

the “Heat” or “Cool” position to activate either heating or

cooling operation, or a positive “OFF” switch on the cooling

thermostat.

Figure 12. Coil Cavity

Damper

Figure 13. Damper without

Coil Cavity

The furnace must also be equipped with an automatic damper

(See Figure 37 or 38, NORDYNE p/n 901996 for furnaces

without coil cavity, or p/n 901083 with coil cavity) to prevent

cold air from being discharged up around the heat exchanger.

Cold air may cause condensation inside the heat exchanger,

which can lead to rust and early failure.

Optional Add-On Air Conditioning – Split Systems

There is a NORDYNE split-system or package air conditioner

designed for your total comfort needs. Whether split system

or single package, an energy-saving NORDYNE unit is avail-

able that has been designed specifically for manufactured

housing applications and can best handle your home comfort

needs.

Listed and ARI Certified, all models are protected by the

NORDYNE Air Conditioner Limited Warranty.

Split system units with vertical discharge for quiet operation

connect to the NORDYNE cooling coil furnace (optional coil

cavity required with “A” model furnaces).

All Weather Cap - Roof Jack Accessories

1. In case of high wind or icy conditions, a 903656 all

weather cap may be needed. See Pilot Outage section.

2. In regions where snow can accumulate and cover any

portion of the roof jack, up to two optional external

extensions can be added — part #901937- each 16” long.

Standing Pilot

Model M1G Furnace

Sequence of Operation

Troubleshooting

Wiring Diagrams

Call for heat,

t-stat closes R-W

Power On

L1 A/C Voltage

Yes

Power up

Selector Switch

Check incoming

power supply to

furnace and

selector switch

Check voltage

at WxC

Power at gas

valve

Check circuit from secondary

voltage through all safety switches

to gas valve

Yes

No No

Gas valve opens

first stage, low fire

Pilot lit

Relight pilot.

Consult "Pilot Outage

Problems" in service

manual

Yes

24 Volts at Gas Valve

Lever in ON Position

Inlet gas pressure OK

Replace Valve

Yes

14 second

second stage

high fire

Yes

Air Circulating

Blower Starts

Yes

Thermostat

Satisfies

Fan Switch

closes at 115˚

Power at

Motor

Yes

Replace

Motor

Replace

Switch

Open R to W

Yes

Shut down,

Replace Thermostat

Air Circulating

Blower Shuts Down

Yes

Stand by

for next cycle

Fan Switch

opens at 95˚

Replace

Switch

Troubleshooting Sequence – M1G 056-070

Call for heat,

t-stat closes R-W

Power On

L1 A/C Voltage

Yes

Power up

Selector Switch

Check incoming

power supply to

furnace and

selector switch

Check voltage

at 1 and 3 on

Combustion Relay

Power at gas

valve

Check circuit from secondary

voltage through all safety switches

to gas valve

Pressure Switch

closes

Refer to Pressure Switch section

Yes

No No

Gas valve opens

first stage, low fire

Pilot lit

Relight pilot

Consult Pilot Outage

section and chart

Yes

24 Volts at Gas Valve

Lever in ON Position

Inlet gas pressure OK

Replace Valve

Yes

14 second

second stage

high fire

Yes

Air Circulating

Blower Starts

Yes

Thermostat

Satisfies

Fan Switch

closes at 115˚

Power at

Motor

Yes

Replace

Motor

Replace

Switch

Open R to W

Yes

Shut down,

Replace Thermostat

Air Circulating

Blower Shuts Down

Yes

Stand by

for next cycle

Fan Switch

opens at 95˚

Replace

Switch

Combustion Air

Motor starts

Refer to Combustion Air Blower

and Blower Relay sections

for troubleshooting

Yes

Refer to Low Voltage and

Limit Control sections

Troubleshooting Sequence – M1G 077-090

Combustion Blower Model

7. Standing Pilot Model M1G

SEQUENCE OF OPERATION FOR STANDING PILOT

a On a call for heat, the thermostat contacts close, supply-

ing 24 VAC to the gas valve.

b. When the gas valve is energized it steps open at a

reduced flow and opens fully after approximately 14

seconds.

c. When the call for heat is satisfied the thermostat contacts

open, the gas valve shuts off gas flow.

SEQUENCE OF OPERATION FOR STANDING PILOT W/

INDUCED DRAFT BLOWERS

a. On a call for heat, the thermostat contacts close, supply-

ing 24 VAC to the relay.

b. The relay contacts close and energize the induced draft

motor.

c. When the motor reaches full speed the pressure switch

closes and energizes the gas valve.

d. When the gas valve is energized it steps open at a

reduced flow and opens fully after approximately 14

seconds.

e. When the call for heat is satisfied the thermostat contacts

open, the gas valve shuts off gas flow, and the induced

draft blower stops.

TROUBLESHOOTING

Polarity and Ground

The furnace will not operate if loss of ground occurs. Every

effort should be made at the installation to provide a good

ground. If old 2-wire romex exists it should be replaced with a

2-wire w/ground. A cold water line could be used provided that

the connection or grounding occurs before any di-electric

fittings and provided no plastic pipe is used inside or outside

the building.

Transformer (Picture 3)

All M1G furnaces are protected by a fuse in the 24 vac circuit.

The transformer supplies control voltage (24 vac) by stepping

down the supply (primary) voltage from 115 vac to 24 vac

(secondary voltage). All M1 transformers are rated at 30 VA.

VA is the volt/amp or total wattage the secondary can handle.

When a transformer is replaced, the VA should be at least 30

VA, but no more than 40 VA.

Check-out procedure:

1. Using a volt/ohmmeter on at least 115 vac scale.

2. Measure the voltage at the primary side.

3. If voltage is 115 vac measure the voltage at the secondary

terminals marked "24 vac" & "Com" on the transformer.

4. If 115 vac is measured at primary but no voltage is present

at "24 vac" & "Com", replace transformer.

5. Fuse will blow if a secondary short occurs.

Transformers open on secondary indicate an overload (a

current draw that exceeded rating).

Picture 3. Transformer

Transformer

Fuse

On-Off Switch (Picture 4) – This switch turns electrical

power to the furnace on and off. The switch must be set in the

“On” position for the furnace to operate. For M1G* models, in

warm weather there is a possibility of the blower coming on

periodically or operating continuously due to a heat buildup

within the furnace by a combination of warm weather and heat

from the pilot. This is normal operation as long as there is

power to the furnace and the On-Off switch is at the “ON”

position. If blower operation is not desired, the On-Off switch

may be set in the “OFF” position to cut the electrical power to

the furnace.

GROUND

NEUT.

HOT

VOLTS AC

VOLTS DC

OHMS

MICRO

AMPS

Volts Com Prep

GROUND

NEUT.

HOT

HOT NEUTRAL

VOLTS AC

VOLTS DC

OHMS

MICRO

AMPS

Volts Com Prep

Polarity may be verified as follows:

1. Turn power supply "ON"

2. Using a voltmeter, check for

voltage between the hot (black)

and neutral (white) wire of

supply circuit.

3. Reading should be Line (Supply)

Voltage.

4. Check for voltage between the

neutral (white) wire and ground

wire of the supply circuit.

5. Reading should be zero volts (if

line voltage is read, polarity is

reversed).

6. Double check by checking for

voltage between the hot (black)

wire and ground wire of the

supply circuit.

Figure 14. Polarity and Ground

Picture 4. On-Off Switch

Low Voltage Wiring – Install the thermostat per the

manufacturer's instructions. The low voltage (24 vac) connec-

tions from the thermostat are made at the terminal strip on the

control board in the furnace. See Figure 4 for the proper

connections for heating only (two-wire) and heating/cooling

(four-wire) applications. The recommended minimum wire

gauge for thermostat wiring is shown in Table 4.

The thermostat must not be installed on an outside wall or any

other location where its operation may be adversely affected.

Adverse effects include radiant loading from fireplaces, sun-

light, or lighting fixtures, and convective loading from warm air

registers or electrical appliances.

To check the heat anticipator setting:

Jump out R to W at thermostat with 10 Loop Helex and

measure current draw after blower starts. Divide by 10.

Example: 4 Amps = .4 set at .4.

Set the heat anticipator according to the manufacturer's

recommendations.

Limit Control (Picture 5) – This furnace is protected by two

high temperature safety limit switches. The auxiliary (upper)

limit switch and the high temperature (lower) limit switch are

automatic reset types. If either limit trips, the burner will shut

off. Check temperature rise and compare to specifications

(45° to 75° F)

Combustion Air Relay – The combustion air relay is used

only on the M1G 077-090. On a call for heat, the relay

activates the combustion air motor. The relay is energized

through the thermostat from the “W” terminal. It has a 24VAC

coil powered by the “W” and Common terminals 3 and 1.

Terminals 4 and 2 are normally open contacts.

Combustion Air Blower – The M1G 077-090 model uses a

combustion air blower incorporated in series with the air inlet

pipe. Its purpose is to supply a forced draft method of

combustion air. The quantity of air is determined by the inlet

orifice ring, located on the inlet to the motor assembly.

Upon a call for heat under normal conditions, the combustion

blower starts up and supplies combustion air to the chamber.

If motor does not start, check to be sure call for heat is

established. See troubleshooting flow chart and sequence of

operation for further details. Then disconnect blower molex

plug and check for voltage at plug. If voltage is available and

motor does not start replace motor. If power is not available

check back through power source and combustion blower

relay contacts. See wiring diagram.

Combustion Motor Assembly Replacement

If, using the information from above, you have determined the

combustion motor assembly needs to be replaced,use the

following procedure:

1. Disconnect Molex plug and pressure switch hoses.

2. Remove screws from the top and break silicone loose

from orifice ring on top side of ventor assembly. (See

Figure 15). Inlet pipe may also break loose, this is normal.

3. Remove screws from bottom of assembly and remove

the whole assembly.

4. Mount new assembly, reattach screws removed in step 3

to bottom. Silicone around bottom, either before or after

installation of combustion air blower.

5. Re-silicone orifice ring and combustion air pipe and

reinstall screws removed in step 2 to top.

6. Reconnect Molex plug and pressure switch hoses from

step 1 and test.

Pressure Switch – The M1G 077-090 uses a differential type

pressure switch. The purpose of this switch is to insure that

a good supply of combustion air is supplied to the burner. The

combustion blower creates a differential in negative pressure

(less than atmospheric pressure) across the orifice ring. The

switch is normally open and closes on a drop in pressure, read

in negative inches of water column.

Picture 5. Fan and Limit Switch

Limit

Switch

Fan

Switch

Figure 15. Combustion Air Blower

Orifice

Ring

Silicone

Under normal operating conditions, once the ventor motor

builds up to speed sufficient differential (negative) pressure

(approximately -0.30” wc) will be created to close the differen-

tial pressure switch and keep it closed the whole heating

cycle. Under abnormal conditions, such as ventor motor

failure, or restricted air inlet or vent, sufficient differential

pressure will not be created.

Pressure switch check out procedure:

1. Remove orange wires from pressure switch. Place tees

in the bases connecting pressure switch to combustion

blower assembly.

2. Connect a differential pressure gauge (magnehelic or

equivalent) to the tees. The magnehelic connection

marked low connects to the lower tee, and the one

marked high connects to the top tee.

3. Start motor.

4. Negative pressure created by the forced draft motor must

be greater than -0.30” w.c. for the switch to close.

5. Use the ohm meter to check for continuity across the

switch.

6. If continuity is established, switch has closed. If ohm

meter shows infinite reading, and a pressure of -.30” w.c.

or higher is present, switch is open, and must be replaced.

If the pressure differential reading will not pull down to -.30”

w.c., possible causes could be:

1. Restriction in air inlet pipe, this causes a greater negative

at the inlet side connection. This will act to open switch. To

prove this, disconnect the hose going to the top connection.

If switch closes, there is too much negative pressure being

created on the inlet side. Look for air inlet restriction.

2. If there is a heat exchanger restriction or exhaust restriction

(any restriction after motor), it will cause a lack of negative

pressure. If flow out of chamber (exhaust) is poor no air

will be drawn in. Clean chamber and recheck.

3. If motor is not running, no negative will be created and

assembly will have to be replaced. (See combustion air

assembly replacement)

Burner Assembly – In order to perform procedures such as

inspecting for presence of LP gas in chamber, changing the

thermocouple, cleaning of pilot and burner, and inspecting the

heat exchanger, the burner assembly must be removed.

Changing Complete Burner Assembly

1. Gas Line - Remove the furnace door then disconnect and

remove the gas line from the valve body by using two

backup wrenches. Be careful not to damage the pipe

threads or introduce dirt into the gas line.

2. Wiring Leads - Remove the two low voltage wiring leads

from the valve body by carefully pulling them off the

connectors. Be careful not to damage or dirty the connector

ends.

3. Main Burner Mounting Plate- Using a philips screwdriver,

remove the screws that hold the main burner mounting

plate to the furnace.

4. Burner Assembly- Slide the burner assembly out from the

furnace.

5. Reverse procedure to reinstall.

NOTE: Be sure to install the gasket. If gasket becomes

damaged or torn, a replacement gasket kit is available.

Contact your distributor for part number.

Table 9. Lower (lesser) Differential Negative Pressure Than Closing Pressure

Insufficient negative pressure measured at the

combustion blower may be caused by:

1. Restriction on outlet side of combustion blower (blocked

flue or debris building up in flue).

2. Leak (lack of restriction) on inlet side. Inducer inlet

leaking, inducer blower props loose or not attached, or

wrong restrictor orifice.

3. To test for restriction in outlet pipe (exhaust) to verify

problem is outside of furnace, disconnect exhaust for

test period only and start furnace. If furnace starts, look

for problem in vent pipe. Reconnect after testing.

Higher than normal negative pressure at top

connection (acts to open switch) may be caused by:

1. Restricted combustion air inlet pipe.

2. To verify if problem is in inlet pipe, disconnect

pressure switch hose at top connection and start

furnace. If furnace starts, look for problems men-

tioned above in inlet pipe. Note: top connection acts

to open contacts on differential switch.

NOTE:

Inlet Pressure - Outlet Pressure = Differential Pressure

Lower (Lesser) Differential Negative Pressure Than Closing Pressure

Before removing burner assembly, shut off all gas

supply and electrical power to the furnace at the main

shut-off.

WARNING:

Gas Valve - The gas valves for the gas furnaces are a 100%

shut-off type and will fail safe if for some reason the gas is

turned off. The valve is a “step-open” type for M1G*-models

– which means it opens to a “low-fire” position, and after 14

seconds, “steps-open” to “high-fire.”

A small orifice is placed in the gas passage to delay the build

up of the working pressure. A minimum of two minutes pause

time is required between cycles to allow the orifice time to

exhaust all working gas from the diaphragm chamber and

obtain full dwell time on subsequent cycles. Factory set

nominal dwell time is approximately 14 seconds and is

not

field adjustable.

Testing Operating Pressure:

a. Remove furnace door and set the gas valve in the OFF

position.

b. Using a 3/16” Allen wrench, remove the plug from the right

side of the valve.

c. Install the barbed adapter in the plug hole. Tighten by

hand at first, then with an open end wrench. Do not

overtighten!

d. Install the hose and manometer to the barbed fitting. Be

sure to check all connections for leaks.

e. Light the pilot by following the instructions on the furnace

and set the gas valve switch to the ON position.

f. With the valve in the ON position, set the thermostat

above room temperature so the furnace will run throughout

the test procedure.

g. With the furnace operating, check for valve staging. The

operating pressure should be approximately 3.5” WC for

Natural Gas, 10” WC for LP gas.

Pilot Assembly, Thermocouple, and Venturi Burner

The pilot lights the main burner. The thermocouple generates

around 30 MV unloaded, (unscrewed from valve) and around

15 MV loaded (screwed into valve). See gas valve and pilot

outage section for troubleshooting.

The pilot orifice is not changed when furnace is converted to

LP (see conversion section). If the flame is more than about

1” in height, it can be adjusted using the pilot adjustment

screw. Turn the screw clockwise to decrease the flow rate,

counterclockwise to increase it. Note: Do not confuse the pilot

adjustment screw with the pressure regulator, which in-

creases by turning clockwise and decreases by turning coun-

terclockwise.

To clean pilot or service thermocouple or burner:

1. Remove burner.

2. Remove pilot assembly screws and pilot shield.

3. Remove pilot tube from pilot assembly.

4. Inspect pilot assembly - tap out pilot orifice and clean or

replace if plugged.

5. Replace the pilot tube, shield, assembly screws, and

burner. Re-start and test.

Figure 16. Burner Assembly with Venturi Assembly

Venturi

Assembly

Picture 7. Gasket

Picture 8. Burner Assembly

Picture 9. Pilot Assembly and Thermocouple

Pilot Assembly

Thermocouple

To change thermocouple:

1. Follow the same steps used to remove pilot assembly

2. Remove pilot tube close-off plate by removing the phillips

screw on the burner plate.

3. Note the height of the thermocouple in relationship to the

pilot before removal. It is critical to use the correct height

for reinstallation. Disconnect thermocouple from gas

valve and pilot assembly.

4. Slide thermocouple out through hole left after pilot close-

off plate was removed.

5. Reinstall new thermocouple and reverse steps from above.

Note: Use hand to tighten thermocouple in gas valve, plus

1/4” turn with wrench. Do not overtighten!

Venturi Burner Assembly

The burner assembly consists of the burner, venturi and

spreader. If burn through or other burner problem occurs,

follow these steps to replace the burner:

1. Follow the steps under changing burner assembly.

2. Disconnect pilot assembly by removing the two screws

holding pilot assembly and shield.

3. Remove the two phillips screws holding the burner from

the round burner plate. Note that one is removed from the

front side and one from the back side.

4. Remove burner and flame spreader assembly.

5. Install the new one by reversing steps 1 through 4.

6. Start up and test.

Gas Valve Replacement

1. Turn off gas and electric.

2. Disconnect the two low voltage wires.

3. Disconnect pilot tubing and thermocouple from gas valve.

4. Remove the two screws from the gas valve mounting

plate.

5. Remove gas valve and remove gas valve mounting.

6. Remove spud holder threaded into valve.

7. Repipe dope spud holder and tighten into new valve.

8. Reverse steps through 5 and test.

Fan Switch (Picture 5) – The fan switch is a temperature

actuated, normally open switch that closes on temperature

rise and is in series with the heating speed of the air circulating

blower. Upon a call for heat, and when the burner builds up

a supply of heat, the fan switch wraps closed at 115° (±5°) and

blower motor starts. After the thermostat opens and the

chamber cools down, the fan switch opens at 95° (±5°) and

blower shuts off.

If blower does not start after warm up, check blower for power.

If blower has power, see Blower Checkout section. If blower

does not have power, check for line voltage across the fan

switch. If voltage is present the switch is open. You also can

remove wires, and ohm out after warm up. NOTE: Use tape

to make sure wires do not touch anything. An infinity reading

indicates the switch is open.

If blower motor does not shut off and chamber has cooled (and

fan switch is off), check across fan switch contacts. If there is

no voltage, pull the single orange wire off (take care not to

touch uninstalled terminal or lay wire against metal). If blower

shuts off, fan switch is stuck closed. If switch does not close

or open properly, it will have to be replaced. Turn off power,

remove wires, and remove the two phillips screws to remove

switch. Install new switch and re-test.

Blower Assembly (Picture 10) – If the blower motor has

power to it (heating speed and neutral) and motor does not

start, motor has electrically opened up. NOTE: Some models

incorporate a capacitor, this should be checked first.

To replace motor:

1. Remove wires going to motor.

2. Remove Phillips screw(s) on left side.

3. Raise entire blower assembly slightly and swing out to left.

4. Loosen set screw on blower hub.

5. Remove screws holding motor to blower housing.

6. Remove motor and replace. NOTE: Some motors are

torsion-flex mount and some are band around mount. See

picture below.

7. Reverse steps 1-5 to reinstall. Note: Be sure to tighten

blower set screw on flat of motor shaft.

Band Around Mount

Picture 10. Blower Assemblies

Torsion Mount

Heat Exchanger Replacement – The heat exchanger is the

largest and most expensive item in the furnace. Before

replacing the heat exchanger, make certain it is the problem.

Call the technical service department if you have any uncer-

tainty about a heat exchanger failure. Heat exchangers can

become sooted up due to debris in top of furnaces,

improper conversion, or not being converted to LP. See

troubleshooting section on flue and conversion section of

this manual. This condition is not covered under warranty.

To Test Heat Exchanger:

Several methods may be used to test, or inspect for heat

exchanger flaws.

1. Remove the blower and burner. Visually inspect the heat

exchanger with a mirror. If you find a crack or hole in any

part of the heat exchanger, replace with out delay.

2. When the blower starts, observe the flame. If there is a

disturbance in the flame, inspect and determine the

cause.

3. Using a CO detector from the nearest register, monitor

the level for an increase while the unit runs. Single digits

of CO are common, but cigarette smoke, etc. can have an

impact on the level. A rapid increase in the CO level while

the furnace is running is not normal. If this occurs inspect

the heat exchanger.

Note: The furnace does not have to removed from its alcove

to replace the heat exchanger. Be sure to order the replace-

ment gasket kit along with the heat exchanger. It contains all

gaskets used in the furnace.

Change Out Procedure:

1. Disconnect all gas and electrical power to furnace.

2. Disconnect flue.

3. Remove burner assembly.

4. a. M1G-056-070 Only: Remove combustion air pipe.

b. M1G-077-090 Only: Remove combustion air pipe and

combustion blower.

5. Remove blower assembly.

6. Remove blower deck panel. NOTE: Panel will be difficult

to remove with furnace in alcove.

7. Remove front panel. NOTE: One of the panel screws is

located through the combustion air box on the right.

8. Lift up divider panel out of side cabinet lances.

9. Support the underside of the heat exchanger with a

board.

10. Remove top collector panel. NOTE: Two screws attach

through top of cabinet.

11. Remove the other eight screws in the top of the cabinet

that hold the combustion air box.

12. Remove heat exchanger and replace.

13. Reverse steps one through eleven to reinstall.

NOTE: Be sure to install all new gaskets (from gasket

replacement kit).

14. Start up and check out for proper operation.

Figure 17. Heat Exchanger

Roll Out Switch - (M1G* - 056 & 070) The furnace is

protected by a manual reset safety switch located on the

bottom left hand side of the combustion pipe. A draft imbal-

ance or improperly staging valve can cause this switch to

open up. Check for poor draft or blockage in the heat ex-

changer to correct draft imbalance.

Pilot Outage – Pilot outage can occur because of either a

mechanical (internal) or environmental (external) problem.

The frequency and conditions that exist will be important

information in solving a pilot outage problem. Most mechani-

cal problems will result in a situation where pilot can not be lit

at all or goes out with the first cycle or shortly thereafter. The

environment around the furnace or home will be trickier to

diagnose and usually will have infrequent occurrences of pilot

outage, such as once a week, only on windy days etc. Since

most pilot outage problems fall under one of these two

situations our troubleshooting will be divided up into these two

areas. See Pilot Outage chart, next page.

Pilot Outage Chart

Problem Possible causes Solutions

Standard crown. Install optional all weather cap.

903656

2. Goes out only when it snows Install optional extension kit

901937

3. Install all weather cap.

903656

4. Install optional HSI conversion kit.

903428

Environmental (external to furnace)

Install optional extension kit to take

both inlet and exhaust above roof

peak.

Roof Jack termination too low, covering

inlet

All the above have been tried with no

resolution.

Goes out only when its windy or

Barometric pressure drops

suddenl

Goes out only in zero or sub-zero

weather

Conditions are such that pilot will

not sta

lit.

Roof jack termination too close to roof line,

causin

downdraft.

Ice forms around air inlet and blocks off

combustion air

Problem Possible causes Solutions

1. No pilot Flame No inlet gas pressure. Check sources.

Plugged pilot orifices. Clean or replace orifices.

Thermocouple burned through. Replace thermocouple if defective.

Millivolts OK-Replace gas valve.

Restricted air inlet or exhaust pipe. Clean out any debris.

No baffle prior to April, 1999. Install baffle kit.

903722

4. Gas valve not staging. Replace gas valve.

5. Gas valve closing improperly Replace valve

Pilot dirty or needs adjustment Adjust or clean pilot

Clean and or adjust pilot. Check inlet

as pressure.

Pilot lights OK, goes out when

main valve comes on or shortly

thereafter

Gas valve not staging or too high inlet gas

pressure.

Replace valve, lower gas pressure at

ulator or house.

Pilot lights with button held, but

oes out when released.

Pilot not contacting 3/8” to 1/2” top of

thermocouple.

Mechanical (Internal to Furnace)

Pilot goes out when main valve

comes on or shortly after, but

only on cold start-up- first cycle

onl

Pilot lights OK, goes out when

as valve closes (pulled out)

Check for proper millivolts - see

thermocouple section for procedure.

7038870

Figure 18. Gas Atmospheric Furnace, M1GH 056, 070 Models

ON/OFF

SWITCH

GAS VALVE

FAN SWITCH

HI-LIMIT

AUX. LIMIT

TRANSFORMER

L1 N

24 V

115 V

WHITE

GRAY

BLUE

BLACK

GRAY

FAN ON/AUTO SWITCH

ORANGE

BLACK

NEUTRAL

GROUND

SCREW

FURNACE ELECTRICAL BOX

BLACK

3A FUSE

BLOWER

MOTOR

HEATING

ONLY

654321

GRAY

RED

BLUE

CONNECTOR

HOUSING CAP

COMMON

FOR OPTIONAL

ACCESSORY KITS

BLACK

LEGENDS

115V: FIELD 115V:

24V: FIELD 24V:

RED

NOTES

1. Incoming power must be polarized. Observe

color coding. (See furnace data label for

electrical information.)

2. If any of the original wires (as supplied with

the appliance) must be replaced, use 105˚C

Thermoplastic type wire or its equivalent.

BLACK

SUPPLIED

BY INSTALLER

BLUE

WHITE

MANUAL RESET

VENT SWITCH

7038890

Figure 19. Gas Atmospheric Furnace, A/C Ready, M1G (B, C, D) 056, 070 Models

RED (LOW)

BLACK (HIGH)

BLUE (MED. HI)

ORANGE (MED. LO)

152

A/C

BLOWER

RELAY

364

ON/OFF

SWITCH

GAS VALVE

FAN

SWITCH

HI-LIMIT

AUX. LIMIT

TRANSFORMER

L1 N

24 V

115 V

BLACK

ORANGE

BLUE

ORANGE

GREEN

WHITE

BLACK

GRAY

BLUE

BLACK

VENT SWITCH

BLUE

FURNACE ELECTRICAL BOX

NEUTRAL

GROUND SCREW

HEATING/

COOLING

HEATING/COOLING

RED

(SEE NOTE)

TIE WIRE

CONNECTOR

HOUSING CAP

BLUE

GRAY

3A FUSE

GRAY

RED

654321

WHITE

654321

RED (LO)

BLACK

(HIGH)

WHITE

SUPPLIED

BY INSTALLER

LEGENDS

115V: FIELD 115V:

24V: FIELD 24V:

NOTES

1. Incoming power must be polarized. Observe color

coding. (See furnace data label for electrical

information.)

2. If any of the original wires (as supplied with the

appliance) must be replaced, use 105˚C

Thermoplastic type wire or its equivalent.

BLOWER

MOTOR

2 SPEED

BLOWER

MOTOR

4 SPEED

BLACK

GRAY

GREEN

WHITE

MANUAL RESET

*M1G(C,D) Heating - replace orange wire with

red wire (low speed)

NOTE: To run at same speed in both heating and cooling mode,

remove wire from either terminal 4 or 6 on the relay, then attach

jumper to terminals 4 and 6.

Figure 21. Standing Pilot with Induced Draft Furnace, A/C Ready M1G (B, C, D) 077, 090 Models

654321

152

A/C

BLOWER

RELAY

364

152

COMBUSTION

BLOWER

RELAY

ON/OFF

SWITCH

GAS

VALVE

HI-LIMIT

AUX. LIMIT

TRANSFORMER

PRESSURE

SWITCH

COMBUSTION FAN

L1 N

24 V

115 V

BLACK

ORANGE

GREEN

WHITE

GRAY

BLUE

GRAY

NEUTRAL

GROUND

SCREW

FURNACE ELECTRICAL BOX

RED

BLACK

BLUE

TIE WIRE

HEATING/

COOLING

BLUE

FAN

SWITCH

BLUE

RED*

CONNECTOR

HOUSING

GRAY

3A FUSE

GREEN

LEGENDS

115V: FIELD 115V:

24V: FIELD 24V:

NOTES

1. Incoming power must be polarized. Observe color

coding. (See furnace data label for electrical

information.)

2. If any of the original wires (as supplied with the

appliance) must be replaced, use 105˚C

Thermoplastic type wire or its equivalent.

BLOWER

MOTOR

SINGLE

SPEED

HEATING/COOLING

654321

RED (LOW)

BLACK (HIGH)

BLUE (MED. HI)

ORANGE

(MED. LO)

WHITE

BLOWER

MOTOR

4 SPEED

654321

RED (LOW)

BLACK (HIGH)

WHITE

CONNECTOR

HOUSING CAP

SUPPLIED

BY INSTALLER

Jumper Wire - M1GB Units Only

Otherwise Hi-Speed Connected

to Blower Relay

GRAY

RED

GREEN

WHITE

BLACK

RED

BLOWER

MOTOR

2 SPEED

7038880

Figure 20. Standing Pilot with Induced Draft Furnace, M1GH 077, 090 Models

152

364

GAS VALVE

FAN

SWITCH

HI-LIMIT

AUX. LIMIT

PRESSURE

SWITCH

COMBUSTION

FAN

L1 N

24 V

115 V

BLACK

BLUE

BLACK

WHITE

GRAY

BLUE

GRAY

SUPPLIED BY

INSTALLER

FAN ON/AUTO

SWITCH

BLUE

BLACK

ORANGE

NEUTRAL

GROUND

SCREW

FURNACE ELECTRICAL BOX

3A FUSE

BUSHING

RED

ON/OFF

SWITCH

CONNECTOR

HOUSING CAP

BLACK

LEGENDS

115V: FIELD 115V:

24V: FIELD 24V:

GRAY

RED

WHITE

BLACK

TRANSFORMER

BLOWER

MOTOR

HEATING

ONLY

654321

BLACK

NOTES

1. Incoming power must be polarized. Observe

color coding. (See furnace data label for

electrical information.)

2. If any of the original wires (as supplied with

the appliance) must be replaced, use 105˚C

Thermoplastic type wire or its equivalent.

Hot Surface Ignition System

Model M1M Furnace

Sequence of Operation

Troubleshooting

Wiring Diagrams

Call for heat,

t-stat closes R-W

Check for red light

on circuit board

24 Volt, C to W

on circuit board

Polarity

is reversed

Switch L1 & L2

Inducer starts

Check fuse on

circuit board,

replace if no

continuity

Check for voltage

at inducer molex plug

Pressure switch

stuck closed

Replace

Board

Replace

pressure switch

Circuit board 3 blinks

Check for voltage

at molex plug

Replace Inducer

Blower

Pressure switch

closes within

10 seconds

Circuit board

blinks 2 times

Is there >8mA on W terminal

of circuit board? Replace t-stat or

add isolation relay.

Pressure switch

open

Inducer pre-purges

for 45 seconds

Greater than

-.30" W.C.

differential at pressure switch

Replace pressure switch

Check venting

Ignitor heats up

and glows for

30 seconds

Gas valve open

Do Burners Light

Ignitor turns off 7 seconds

after gas valve opens

Main blower starts after

delay time (30 seconds)

Flame, inducer, main blower

stay on until call for heat ends

Replace ignitor

Replace circuit board

24 volts at gas valve.

Insure lever is in

ON position. Insure gas inlet

pressure is below 14" W.C.

Replace gas valve

Manifold Gas

Pressure Available

Burners stay on

longer than 6 seconds

Check and adjust ignitor

gap to 5/16"

Will retry 4 more times.

Soft lock out blinks 4 times

on status light.

Power down and

back up to reset.

Replace board

Flame light on

Replace circuit board

Check for voltage at

com and heat terminals

Replace circuit board

Yes

Check motor

and capacitor

Yes

Flashing

OFF

Is light blinking

5 times?

Adjust ignitor gap to 5/16"

Check ground circuit to

Furnace.

Flame light blinks at

1 uA(weak signal)

Note:

Retry

Every

Hour

Inducer post-purges

for 30 seconds

Main Blower Fan Off Timing

Troubleshooting Sequence – M1M

8. Hot Surface Ignition System

Model M1M

SEQUENCE OF OPERATION M1M SERIES

Call for heat: the thermostat calls for heat by energizing the

“W” terminal. The control checks to see the pressure switch

is open. If the pressure switch is closed when the call for heat

occurs, the control will begin to flash “3” on the Status LED

after 10 seconds and wait indefinitely for the pressure switch

to open.

Pressure switch proving: the control energizes the induced

draft motor and waits for the pressure switch to close. If the

pressure switch does not close within 10 seconds of the

inducer energizing, the control will begin to flash “2” on the

Status LED and wait indefinitely for the pressure switch to

close.

Pre-purge: the control runs the inducer for a 45 second pre-

purge time.

HSI warm up: the control energizes the HSI for 30 seconds.

The inducer remains energized.

Ignition activation period: the control energizes the main gas

valve for 6 seconds. The inducer and HSI remain energized.

Flame proving: the control de-energizes the hot surface

ignitor. The gas valve and inducer remain energized. If flame

is present 1 second after HSI de-energizes, the control goes

to blower on delay. If a flame is not present, the control de-

energizes the gas valve and proceeds with ignition retries as

specified below.

Blower on delay: If flame is present, the control energizes the

blower on HEAT speed 30 seconds after the gas valve

opened (24 seconds from HSI off). The gas valve and inducer

remain energized.

Steady heat: Control inputs are continuously monitored to

ensure limit and pressure switches are closed, flame is

established, and the thermostat call for heat remains.

Post purge: When the thermostat demand for heat is satisfied,

the control de-energizes the gas valves. The inducer output

remains on for a 30 second post-purge period.

Blower off delay: The indoor blower motor is de-energized

after a 120 second blower off delay. Blower timing begins

when the thermostat is satisfied.

COMPONENT PARTS

TROUBLESHOOTING

Polarity and Ground

The furnace will not operate if loss of ground occurs. Every

effort should be made at the installation to provide a good

ground. If old 2-wire romex exists it should be replaced with a

2-wire w/ground. A cold water line could be used provided that

the connection or grounding occurs before any di-electric

fittings and provided no plastic pipe is used inside or outside

the building.

Transformer (See Figure 21) – The transformer supplies

control voltage (24 vac) by stepping down the supply (pri-

mary) voltage from 115 vac to 24 vac (secondary voltage).

Transformers are rated by VA. VA is the volt/amp or total

wattage the secondary can handle. When a transformer is

replaced the VA should be of an equal or greater value.

Check-out procedure:

1. Using a volt/ohmmeter on at least 115 vac scale.

2. Measure the voltage on the control board terminals

"XFMR" & "NEUTRAL".

3. If voltage is 115 vac measure the voltage at terminals

marked "24 vac" & "Com" located in the center of the

control board.

4. If 115 vac is measured at "XFMR" & "NEUTRAL" but no

voltage is present at "24 vac" & "Com" replace transformer.

GROUND

NEUT.

HOT

VOLTS AC

VOLTS DC

OHMS

MICRO

AMPS

Volts Com Prep

GROUND

NEUT.

HOT

HOT NEUTRAL

VOLTS AC

VOLTS DC

OHMS

MICRO

AMPS

Volts Com Prep

Polarity may be verified as follows:

1. Turn power supply "ON"

2. Using a voltmeter, check for

voltage between the hot (black)

and neutral (white) wire of

supply circuit.

3. Reading should be Line (Supply)

Voltage.

4. Check for voltage between the

neutral (white) wire and ground

wire of the supply circuit.

5. Reading should be zero volts (if

line voltage is read, polarity is

reversed).

6. Double check by checking for

voltage between the hot (black)

wire and ground wire of the

supply circuit.

Figure 22. Polarity and Ground

Picture 11. M1M Transformer

Transformers open on primary indicate low voltage short

circuit. Transformers open on secondary indicate an overload

(a current draw that exceeded rating).

Low Voltage Wiring

Install the thermostat per the manufacturer's instructions. The

low voltage (24 vac) connections from the thermostat are

made at the pigtail wires coming off the control board in the

furnace. See Figure 23 for the proper connections for heating

only (two-wire) and heating/cooling (four-wire) applications.

The recommended minimum wire gauge for thermostat wiring

is shown in Table 5.

The thermostat must not be installed on an outside wall or any

other location where its operation may be adversely affected.

Adverse effects include radiant loading from fireplaces, sun-

light, or lighting fixtures, and convective loading from warm air

registers or electrical appliances.

To check the heat anticipator setting:

Jump out R to W at thermostat with 10 Loop Helex and

measure current draw after blower starts. Divide by 10.

Example: 4 Amps = .4 set at .4.

Limit Control (Picture 14) – This furnace is protected by two

high temperature safety limit switches. The auxiliary (upper)

limit switch and the high temperature (lower) limit switch are

automatic reset types. If either limit trips, the burner will shut

off, and status light will flash “1”.

M1M-Control Board Replacement

Replace the control board only after determining a failure has

occurred in it. Most problems that are blamed on control are

actually external to control. (See troubleshooting section). If

control has failed, use the following procedure to replace.

1. Disconnect power to unit by turning off power switch.

2. Disconnect molex plugs and all push on terminal

connections. Note connections for rehook up.

3. After all wire connections have been removed you must

squeeze the four white stand offs to remove board. See

Pictures 13 showing board removed with exposed

standoffs remaining.

4. Carefully line up holes (Picture 12) on the new board over

standoffs, and push into place. Caution: push from

outside edge only - be careful of fragile components.

5. Reinstall all molex plugs and wires removed in step 2.

6. Apply power and re-test.

Ignition Control Troubleshooting

RED

Steady ON Control OK

Steady OFF No power

Rapid Flash False flame or internal control fault

1 Flash Limit switch is open

2 Flashes Pressure switch is open with inducer on

3 Flashes Pressure switch is closed with inducer off

4 Flashes Lockout due to failed ignition

5 Flashes 115 vac & neutral reversed or no ground

YELLOW

Steady ON Good Flame Signal

Blinking Weak Flame Signal

Steady OFF No Flame Signal

CONTROL LIGHT STATUS

Picture 14. Limit Switch

Picture 12. UTEC Ignition Control

Stand off

Holes

Picture 13. Ignition Board Removed

Stand offs

1. Power Line Polarity – The “hot” side of the power line

must be connected to the “L1” for the control to be able to

sense flame. The control detects the reversal of “hot” and

neutral. When L1 and Neutral are switched (or L1 is not

present), the control flashes “5” on the Status LED and

locks out.

2. Interrupted Thermostat – If the thermostat demand for

heat is removed before the flame recognition period, the

control will run the inducer for the post purge period and

de-energize all outputs.

3. Ignition Re-Try – If flame is not established on the first

trial for ignition period, the gas valve is de-energized and

the inducer remains energized for an inter-purge period of

30 seconds. The ignitor is then re-energized and the

control initiates another trial for ignition. This sequence

repeats for up to 5 trials for ignition.

4. Ignition Re-Cycle – Flame must not be sensed for 1

second before the control responds to a loss of flame. If

flame is established and maintained during the trial for

ignition period and then flame is lost, the gas valve is de-

energized within 2 seconds, the induced draft motor

continues to run, and the control begins timing the 45

second inter-purge delay. The indoor blower motor will be

energized and/or remain energized on heat speed for the

selected delay off time.

When the inter-purge delay is over, the ignitor is re-

energized, and the control initiates another ignitor warm

up and ignition activation period. The control will re-cycle

up to 5 flame losses (4 re-cycles) within a single call for

heat before going to lockout.

5. Call for Continuous Fan/Cooling – When a thermostat

call for continuous fan (G) without a call for heat or

cooling, the indoor fan is energized on the COOL speed

after a .25 second delay. If a call for heat (W) occurs

during continuous fan, the blower will de-energize.

A call for fan is ignored while in lockout.

6. Limit Switch Operation – Any time the limit switch

opens, the gas valve and ignitor will be de-energized, the

indoor blower motor will run on heat speed, and induced

draft motor will run continuously. Control status LED

flashes “1.”

When the switch re-closes, the induced draft motor will

run through post-purge and the indoor blower will run

through the selected fan off delay. The control will return

to normal operation after the blower off delay is completed.

7. Pressure Switch – The control shall ignore pressure

switch openings of less than 1 second (the gas valve will

momentarily de-energize while the pressure switch is

open, this may cause a loss of flame). To prevent pressure

switch faults from being treated as flame losses, the

control checks to see if the pressure switch has been

open momentarily within 2 seconds prior to the flame loss.

If the pressure switch was open any time within the 2

seconds prior to a flame loss, the control assumes the

flame loss was due to the open pressure switch and

responds as described below.

If the pressure switch opens for more than 1 second after

flame has been established, the control shall de-energize

the gas valve, run through a normal 30 second post-purge

and selected heat blower off delay. When the blower off

delay is complete, the control shall start an ignition

sequence if the thermostat is still calling for heat.

If the pressure switch opens for more than one second

during a pre-purge or inter-purge, the control shall wait for

the pressure switch to close. The purge time re-starts

when the pressure switch closes. The control status LED

will flash “2.” If the pressure switch is closed when the call

for heat occurs, the control will begin to flash “3” on the

status LED after 10 seconds and wait indefinitely for the

pressure switch to open.

8. Flame sense – Flame is normally sensed through the hot

surface ignitor using flame rectification. Open circuit

flame sense voltage should be approximately 120 VAC

line voltage. Minimum flame current required to sense

flame is 0.5 microamps DC. Normal microamps is 3 or

higher. To test, install microamp meter in series with

ground (9) pin. If flame light is on solid microamp signal is

at least 1 microamp. If flame light is blinking, flame signal

is between 0.5 and 1 microamp, indicating a weak signal.

Check for ignitor positioning and proper ground.

9. Undesired Flame – If flame is sensed longer than 4

seconds while the gas valve is de-energized, the control

shall energize the induced draft motor and indoor blower

on heat speed. When flame is no longer sensed, the

induced draft motor will run through post-purge and the

indoor blower motor will run through the selected heat fan

off delay time. The control will do a soft lockout, but will still

respond to open limit and flame. The Status LED will flash

rapidly when lockout is due to undesired flame.

10. Lockout – The control shall not initiate a call for heat or

call for continuous fan while in lockout. A call for cooling

operates as normal. The control will still respond to an

open limit and undesired flame.

Lockout will automatically reset after 1 hour. Lockout may

be manually reset by removing power from the control for

more than 1 second or removing the thermostat call for

heat for more than 1 and less than 20 seconds (The 20

second time limit prevents electronic thermostats from

automatically resetting lockout).

11. Power Interruption – The control will not interrupt its

operational sequence from power interruptions less than

80 mS in duration. Relay outputs will momentarily de-

energize during the interruption.

Power interruption greater than 80mS may cause the

control to interrupt the operating sequence and resume

as if power was first applied. All power interruptions of any

duration are to be self recovered and not result in a

condition that could cause lockout.

12. Control Internal Diagnostics

a.) Internal microprocessor tests: The software will

perform tests of the internal microprocessor hardware as

much as is practical. A detected failure in internal hardware

will result in lockout with the Status LED blinking rapidly.

b.) Flame sense circuitry diagnostics: The integrity of the

flame sense circuitry is constantly monitored by the

microcontroller. The control will lock out with the status

LED flashing rapidly if a fault is detected in the flame

sense circuitry.

c.) Failed gas valve relay: If the control senses the gas

valve output as energized when it should be de-energized,

and flame is not present, the control shuts off all control

outputs (including the inducer motor) to force the pressure

switch to open. If gas valve remains sensed as energized

15 seconds after the inducer shut off, the inducer is re-

energized to attempt to vent the uncontrollable gas.

If the control senses the gas valve output as energized

when it should be de-energized, and flame is present, the

control keeps the inducer motor and indoor blower motor

energized until flame is removed.

If the control does not sense that the gas valve is energized

when it should be, the control locks out with the Status

LED flashing rapidly.

Combustion Air Blower – All M1M models use a combustion

air blower incorporated in series with the air inlet pipe. Its

purpose is to supply a forced draft method of combustion air.

The quality of air is determined by the inlet orifice ring, located

on the inlet to the motor assembly.

Upon a call for heat under normal conditions, the combustion

blower starts up and supplies combustion air to the chamber.

If motor does not start, check to be sure call for heat is

established and fault light is on solid. See troubleshooting

flow chart and sequence of operation for further details. Then

disconnect blower molex plug and check for voltage at plug.

If voltage is available and motor does not start replace motor.

If power is not available check back through power source and

combustion blower relay contacts. See wiring diagram.

Picture 18. Blower Open Motor

Picture 17. Blower OHM

Picture 15. Combustion Air Blower

Figure 23. Combustion Air Blower

Orifice

Ring

Silicone

Picture 16. Blower Voltage

Combustion motor assembly replacement

Using the information from above you have determined the

combustion motor assembly needs to be replaced, follow the

outlined procedures.

1. Disconnect Molex plug

2. Remove screws from the top and break silicone loose

from orifice ring on top side of ventor assembly. Figure

Picture #26 inlet pipe may also break loose, this is

normal.

3. Remove screws from bottom of assembly and remove

the whole assembly.

4. Mount new assembly, reattach screws to bottom remove

from step 3.

5. Re-silicone orifice ring and combustion air pipe and

reinstall screws to top removed in step 2.

6. Reconnect Molex plug from step 1 and test.

Pressure Switch (Picture 19) – All M1M furnaces use a

differential type pressure switch. The purpose of this switch

is to insure that a good supply of combustion air is supplied

to the burner. The combustion blower creates a differential

in negative pressure (less than atmospheric pressure) across

the orifice ring. The switch is normally open and closes on a

drop in pressure, read in negative inches of water column.

Under normal operating conditions, once the ventor motor

builds up to speed sufficient differential (negative) pressure

(approximately -0.30” wc) will be created to close the differen-

tial pressure switch and keep it closed the whole heating

cycle. Under abnormal conditions, such as ventor motor

failure, or restricted air inlet or vent, sufficient differential

pressure will not be created.

Under most circumstances, when the pressure switch is not

going closed, insufficient differential (negative) pressure is not

being created. See Table 9 for opening and closing settings.

Pressure switch check out procedure:

1. Remove orange wires from pressure switch. Place tees

in the bases connecting pressure switch to combustion

blower assembly.

2. Connect a differential pressure gauge (magnehelic or

equivalent) to the tees. The magnehelic connection

marked low connects to the lower tee, and the one

marked high connects to the top tee.

3. Start motor.

4. Negative pressure created by the forced draft motor must

be greater than -0.30” w.c. for the switch to close.

5. Use the ohm meter to check for continuity across the

switch.

6. If continuity is established, switch has closed. If ohm

meter shows infinite reading, and a pressure of -.30” w.c.

or higher is present, switch is open, and must be replaced.

If the pressure differential reading will not pull down to -.30”

w.c., possible causes could be:

1. Restriction in air inlet pipe, this causes a greater negative

at the inlet side connection. This will act to open switch. To

prove this, disconnect the hose going to the top connection.

If switch closes, there is too much negative pressure being

created on the inlet side. Look for air inlet restriction.

Table 9. Lower (lesser) Differential Negative Pressure Than Closing Pressure

Insufficient negative pressure measured at the

combustion blower may be caused by:

1. Restriction on outlet side of combustion blower (blocked

flue or debris building up in flue).

2. Leak (lack of restriction) on inlet side. Inducer inlet

leaking, inducer blower props loose, or wrong restrictor

orifice.

3. To test for restriction in outlet pipe (exhaust) to verify

problem is outside of furnace, disconnect exhaust for

test period only and start furnace. If furnace starts, look

for problem in vent pipe. Reconnect after testing.

Higher than normal negative pressure at top

connection (acts to open switch) may be caused by:

1. Restricted combustion air inlet pipe.

2. To verify if problem is in inlet pipe, disconnect

pressure switch hose at top connection and start

furnace. If furnace starts, look for problems men-

tioned above in inlet pipe. Note: top connection acts

to open contacts on differential switch.

NOTE:

Inlet Pressure - Outlet Pressure = Differential Pressure

Lower (Lesser) Differential Negative Pressure Than Closing Pressure

Picture 19. Pressure Switch

2. If there is a heat exchanger restriction or exhaust restriction

(any restriction after motor), it will cause a lack of negative

pressure. If flow out of chamber (exhaust) is poor no air

will be drawn in. Clean chamber and recheck.

3. If motor is not running, no negative will be created and

assembly will have to be replaced. (See combustion air

assembly replacement)

Hot Surface Ignitor – The hot surface ignitor is helical in

shape and is located approximately 5/16" in front of the

burners. Its function is to ignite fuel at the appropriate time in

the sequence. The hot surface ignitor used is manufactured

by CARBORUNDUM.

NOTE: Special care should be taken when handling the ignitor.

You should never touch the ignitor surface. Grease or dirt from

your hands will shorten the ignitor's life.

Check-out Procedure:

1. Unplug ignitor from 2-prong plug.

2. Place a voltmeter on the proper scale (at least 115 vac).

3. Establish a call for heat.

4. After approx. 45 seconds of induced draft motor operation,

the ignitor should see line voltage.

5. If voltage is present, replace the ignitor. (See Figure 41.)

6. If no voltage is present, replace control board.

7. The ignitor may also be ohmed out. The ignitors usually

range from 125 to 150 ohms at 70°F/21°C.

8. Be sure when replacement ignitor is installed that it is

approximately 5/16" from the burners. Mishandling and

misalignment are the primary causes of ignitor failure.

Picture 20. Hot Surface

Ignitor

Picture 21. Ignitor and

Voltmeter

Picture 22. Test Hot Surface Ignitor

Figure 24. M1M Burner Assembly

Burner Assembly – In order to perform procedures such as

inspecting for presence of LP gas in chamber, cleaning

burner, and inspecting the heat exchanger, the burner assem-

bly must be removed.

Changing Complete Burner Assembly

1. Gas Line - Remove the furnace door then disconnect and

remove the gas line from the valve body by using two

backup wrenches. Be careful not to damage the pipe

threads or introduce dirt into the gas line.

2. Wiring Leads - Remove the two low voltage wiring leads

from the valve body by carefully pulling them off the

connectors. Be careful not to damage or dirty the connector

ends.

3. Main Burner Mounting Plate- Using a philips, remove the

screws that hold the main burner mounting plate to the

furnace.

4. Burner Assembly- Slide the burner assembly out from the

furnace.

5. Reverse procedure to reinstall.

NOTE: Be sure to install the gasket.

Gas Valve - The gas valves for the gas furnaces are a 100%

shut-off type and will fail safe if for some reason the gas is

turned off.

When the thermostat calls for heat, the first and second valves

open by the energization of two solenoids. If 24 vac is

available at valve and no gas flows, valve is defective. NOTE:

Be sure gas pressure is available at the inlet to the valve and

does not exceed 14” w.c. (1/2 lb.). If this condition exists, valve

will lock down and no gas will flow through it.

Step Flow: during the dwell time, there is no flow through the

main valve since it is closed. A calibrated bypass hole provides

step flow, for soft ignition and draft build up, during the dwell

time. The bypass flow can be custom tailored from 40% to 70%

of full flow, but is also

not

field adjustable. At the end of the dwell

time, the main valve opens, allowing full gas flow.

Testing Operating Pressure:

a. Remove furnace door and set the gas valve in the OFF

position.

b. Using a 3/16” Allen wrench, remove the plug from the right

side of the valve.

c. Install the barbed adapter in the plug hole. Tighten by

hand at first, then with an open end wrench. Do not

overtighten!

d. Install the hose and manometer to the barbed fitting. Be

sure to check all connections for leaks.

e. Set the gas valve switch to the ON position.

f. With the valve in the ON position, set the thermostat

above room temperature so the furnace will run throughout

the test procedure.

g. With the furnace operating, check for valve staging. The

operating pressure should be 3.5” WC for Natural Gas,

10” WC for LP gas.

Blower Assembly – If the blower motor has power to it

(heating speed and neutral) and motor does not start, motor

has electrically opened up. NOTE: Some models incorporate

a capacitor, this should be checked first.

To replace motor:

1. Remove wires going to motor.

2. Remove single Phillips screw in upper left corner.

3. Raise entire blower assembly slightly and swing out to left.

4. Loosen set screw on blower hub.

5. Remove screws holding motor to blower housing.

6. Remove motor and replace. NOTE: Some motors are

torsion-flex mount and some are band around mount. See

picture below.

7. Reverse steps 1-5 to reinstall. Note: Be sure to tighten

blower set screw on flat of motor shaft.

Heat Exchanger Replacement – The heat exchanger is the

largest and most expensive item in the furnace. Before

replacing the heat exchanger, make certain it is the problem.

Call the technical service department if you have any uncer-

tainty about a heat exchanger failure. Heat exchangers can

become sooted up due to debris in top of furnaces,

improper conversion, or not being converted to LP. See

troubleshooting section on flue and conversion section

of this manual. This condition is not covered under

warranty. See page 22 of this manual – To Test Heat

Exchanger.

Note: The furnace does not have to removed to replace the

heat exchanger.

Change Out Procedure:

1. Disconnect all gas and electrical power to furnace.

2. Disconnect flue.

3. Remove burner assembly.

4. Remove combustion air pipe and combustion blower.

5. Remove blower assembly.

6. Remove blower deck panel. NOTE: Panel will be difficult

to remove with furnace in alcove.

7. Remove front panel. NOTE: One of the panel screws is

located through the combustion air box on the right.

8. Lift up divider panel out of side cabinet lances.

9. Support the underside of the heat exchanger with a

board.

10. Remove top collector panel. NOTE: Two screws attach

through top of cabinet.

11. Remove the other eight screws in the top of the cabinet

that hold the combustion air box.

12. Remove heat exchanger and replace.

13. Reverse steps one through eleven to reinstall.

NOTE: Be sure to install all new gaskets (from gasket

replacement kit).

14. Start up and check out for proper operation.

Picture 23. Blower Assemblies

Band Around Mount

Torsion Mount

Figure 25. Heat Exchanger

ORANGE

BLOWER

MOTOR

SINGLE

SPEED

ON/OFF

SWITCH

GAS VALVE

HI-LIMIT

AUX. LIMIT

TRANS-

FORMER

PRESSURE

SWITCH

654321

COMBUSTION FAN

L1 N

24 V

115 V

IGNITOR

BLUE

BLACK

GREEN

YELLOW

BLACK

ORANGE

BLACK

WHITE

NEUTRAL

GROUND SCREW

FURNACE ELECTRICAL BOX

24V

NEU

XFRM

TIE

WIRE

RED

BLACK

BLUE

CONNECTOR

HOUSING CAP

GROUND

SCREW

BLACK

CONTROL LIGHT STATUS

RED YELLOW

Steady ON Control OK Steady ON Good Flame Signal

Steady OFF No power Blinking Weak Flame Signal

Rapid Flash False flame or internal control fault Steady OFF No Flame Signal

1 Flash Limit switch is open

2 Flashes Pressure switch is open with inducer on

3 Flashes Pressure switch is closed with inducer off

4 Flashes Lockout due to failed ignition

5 Flashes 115 vac & neutral reversed or no ground

CONTROL

LIGHTS

RED

Jumper must be

removed if converting

to a multispeed blower.

Jumper is required for

M1MA models and

M1MB 077, 090

BLACK

WHITE

BLACK

GREEN

RED

GRAY

WHITE

BLACK (HIGH)

RED (LO)

WHITE

RED (LO)

BLACK (HIGH)

BLUE (MED. HI)

ORANGE (MED. LO)

WHITE

654321

LEGENDS

115V: FIELD 115V:

24V: FIELD 24V:

BLOWER

MOTOR

2 SPEED

BLOWER

MOTOR

4 SPEED

NOTES

1. Incoming power must be polarized. Observe color

coding. (See furnace data label for electrical

information.)

2. If any of the original wires (as supplied with the

appliance) must be replaced, use 105˚C Thermoplastic

type wire or its equivalent.

SUPPLIED

BY INSTALLER

C W G R

COM

BLUE

WIRING DIAGRAM

7038540

Figure 25. Gas Direct Ignition Furnace, Heating & A/C Ready - All M1M Models

UTEC M1 FURNACE CONTROL SEQUENCE

Start-Up / Shut-Down

Thermostat on

call for heat

(R to W)

Event

Inducer

Igniter

Main Blower

Flame Proving

Gas Valve

Main Blower

Gas Valve

Factory Set

at 120 seconds

Elapsed Time Line - Seconds

Thermostat Off

(Break R to W)

Inducer

1200

112

NORMAL START-UP SEQUENCE

Elapsed Time Line - Seconds

NORMAL SHUT-DOWN SEQUENCE

Normal Start-Up:

1. Close R to W circuit. The inducer motor is energized.

2. After a 45 second pre-purge the igniter is energized.

3. After a 30 second heat up the gas valve is energized (The igniter remains on during

the first 6 seconds. Gas valve will be de-energized at 7 seconds if flame is not proved.)

4. After 30 seconds the main blower is energized. (Total elapsed time 105 seconds).

Normal Shut-Down:

1. Break R to W circuit.

2. After 30 seconds the inducer is turned off.

3. After 90 seconds the main blower is turned off (120 seconds after gas valve).

St. Louis, MO

690A-0999 (Replaces 690A-0998)

Specifications and illustrations subject to change

without notice and without incurring obligations.

Printed in U.S.A. (09/99)