Nordyne M1G User manual

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
A.
B.
C.
D.

3
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
Roofjacktroubleshooting......................................... 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

4
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
Thisservicemanualisdesignedtobeusedinconjunctionwith
the installation manual provided with each furnace.
The downflow sealed combustion furnaces illustrated in this
servicemanualrepresenttheverylatestinhighefficiencygas
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.
Thismanualwilldealwithallsubjectsinageneralnature(i.e.
alltextwill pertaintoall models) unlessthatsubject isunique
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
byaqualifiedservicetechnicianwhoisfamiliarwiththesafety
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
suchrepairs to the risk of injury or electrical shockwhich 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

5
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,andoperatingefficiencyoftheseappliances.Improper
installationmaycreatehazardousconditions,andwillvoidthe
appliance warranty.
1. SPECIFICATIONS
GENERAL DESCRIPTION
M1 Series gas and oil furnaces are listed direct vent (sealed
combustion),downflowheating appliancesformanufactured
(mobile)homes,recreationalvehicles,andforuseinresiden-
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-speedblowerassemblies(SeeAccessories)havebeen
certified for field installation in M1 Series furnaces. An air
conditioner can be easily field installed with M1GH Series
furnacesifusedinconjunctionwithcertified2-wirerelaybox,
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
installationshallbeinaccordancewiththecurrentprovisions
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
ModelNo MBtu/h MBtu/h Nat. LP InWC 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

6
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. AmericanNationalStandard(ANSI-Z95.1/NFPA-31)and/
or CSA B139 for all oil-fired furnace models.
e. AmericanNationalStandard(ANSI-C1/NFPA-70)and/or
CSA22.1Canadian ElectricCodePart 1 forallelectrical
field wiring.
f. Units have been investigated under standards UL 307A
&B,ANZI21.47a—CAN/2.3a-1995,andCSAB140.10.
2. CIRCULATING AIR SUPPLY
RETURN AIR PROVISIONS
U.S.A. home manufacturers shall comply with all of the
followingconditionstohave acceptablereturnairsystemsfor
closet installed forced air heating appliances:
a. Regardlessofthelocation,thereturnairopeningintothe
closet shall not be less than specified in the appliance’s
listing.
b. Means shall be provided to prevent inadvertent closure
bya flat objectplaced over thereturn air openingwhen it
islocatedinthefloorofthecloset(versustheverticalfront
or side wall).
c. The cross-sectional area of the return duct system lead-
ingintothecloset,whenlocatedinthefloororceilingshall
notbelessthan235squareinches(or390squareinches
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
whereitisnotlikelytobecoveredbycarpeting,boxesand
other objects.
e. Materials located in the return duct system must have a
flamespreadclassificationof200orless.Thisincludesa
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

7
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. Gaspipingisnotruninorthroughthereturnductsystem.
i. Test the negative pressure in the closet with the air-
circulating fan operating at high speed and the closet
closed.Thenegativepressureistobenomorenegative
than minus 0.05 inch water column.
j. Forfloorreturnsystems,themanufacturedhomemanu-
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. Airconditioningsystemsmayrequiremoreduct,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
designedsothatthestaticpressuremeasuredexternaltothe
furnace does not exceed the listed static pressure rating
shown on the furnace rating plate.
Before installing an air conditioner system, consult home
manufacturerforductsystemmaximumcapacity. Location,
size,andnumberofregistersshouldbeselectedonthebasis
of best air distribution and floor plan of the home.
Table 3. Roof Jack Assemblies
CAUTION:
HAZARDOFASPHYXIATION:Donotcoveror
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
openingtocenterofceilingopening.(SeeDimension“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
ifslantdeck flashingisused). The totallengthof (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)thatismadeupofapipewithinapipeconstruction.
Theinner pipe(5”)is fortheflue gasesto exit thehome. The
outerpipe(8”)isusingthespacein-betweenthe5”and8”pipe
forcombustionair. Ifthefurnaceissmotheringitselfout,after
ashorttime,onnaturaldraftmodels,orpressureswitchdoes
notmakecontactonM1Mmodel,slideupairinletafewinches
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
removetopandmakesurenoseamshaveopeneduponroof-
jackassembly. OntheM1Gfurnace(naturaldraftmodel)the
airinletlimittrippingiscausedfromaunbalanceddraft,which
means the air inlet becomes a better flue than the flue itself.
Check-out Procedure:
Is furnace filter clean?
Iffurnaceisinstalledincloset,whatisthelouveropenarea?
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 T27 47 - 2
AW= ALL WEATHER
FLASHING
PITCH/12" RISE
0=FLAT
2=2.5/12
4=4/12
MIN. ADJ.
LENGTH
F=
S= 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"

8
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.
Isthe burneralignedperpendicular totheburner 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)willalsohelp(seePilotOutage).SeeAccessory
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. Iftheroofjackcrowniscoveredorblockedwithsnow,the
furnacewillnotoperateproperly.Ifthehomeislocatedin
regions where snow accumulation exceeds 7” (HUD
snowloadzones) use anexternal roof jackextension 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”).
Internalroofjackextensions(p/n901935-10”,p/n903107
-18”)canbeusedtoincreaseroofjackheight.Allconnec-
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.Alllinevoltageconnectionsmustbemadewithinthe
junction box located within the furnace.
The furnace cabinet must have an uninterrupted, unbroken
ground to minimize injury should an electrical fault condition
occur.Thecontrolsused in thisfurnacealsorequirean earth
groundtocooperateproperly.Acceptablemethodsforground-
ingareelectricalwireorconduitapprovedforelectricalground
service. Do not use gas piping as an electrical ground.
NOTE:Properlinevoltagepolaritymustbemaintainedin
order for the control system to operate correctly. Verify
that the incoming neutral line is connected to the white
wireandtheincoming"hot"lineisconnectedtotheblack
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
2
SLANT DECK
/12
12
ROOF JACK WITH
2
FLASHING
/12 SLANT
12
ROOF JACK
SLANT DECK
FLASHING
PITCHED
ROOF
CEILING
CEILING CAVITY
ROOF OPENING
CEILING OPENING
"X" (SEE TABLE 1)
6

9
Supply Voltage
Supply voltage to the furnace should be nominal 115 volts. It
mustbebetween103voltsand127volts.Supplyvoltagetothe
furnaceshouldbecheckedwithfurnaceinoperationandblower
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
sourcesofheatorcolddrafts. Thenominalanticipatorsetting
is 0.4. (Refer to the thermostat literature for additional infor-
mation.)
Five-conductor thermostat wire is recommended for 24 volt
low-voltagecircuit (2-wireis required forfurnace only;5-wire
for heating and optional cooling systems).
Oncethefurnaceisinstalledcheckthethermostatanticipator
against the nominal setting of 0.4:
1. Connectthemilliamp meter inseries withthe “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.
Ifthe heatanticipatoris settoo highthefurnace maydelay 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
g
th
(
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
Rc
R
H
W
G
Y
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 Ground Ground

10
f. It is not necessary to convert the pilot orifice.
g. For Honeywell gas valves with the regulator converter
(Figure8),checkforthelettersNATorLPonthepressure
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
bottomandthe“LP”stampingontheconverterwillappear
right side up.) Then screw converter back into the regu-
lator,handtightplus1/8turn,andreplacetheblackcover
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. Openthemanualshut-offvalveandfollowtheFURNACE
START-UPprocedureasoutlinedpreviouslyinthismanual
to put the furnace into operation.
NOTE:Thepilotflameisadjustablebyturningtheadjustment
screwlocatedonthegasvalvewithasmallscrewdriver.(See
Figure 10)
5. GAS SUPPLY, CONVERSION, AND
LIGHTING – M1G AND M1M MODELS
GAS PIPING
Sizingandinstallationoffuellinesmustbeinaccordancewith
federal, state and local regulations. All piping shall be black
ironpipe, orequivalently sizedsteel tubing. Internallytinned
copper tubing may be used for gas supply systems.
Fuellineinstallationsotherthantypicalinstallationsshownin
Figure7mustcomplywiththefuelpipingprovisionsstatedin
theFederalManufacturedHomeStandard(H.U.D.TITLE24,
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. Thenecessaryinstructionsforthegasconversionare
foundonthelightinginstructionlabelattachedtothefurnacein
Section 16, Service Guide.
Fornaturalgasoperation,thefurnaceisdesignedfor7"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
Thisgasfiredheatingappliancewasshippedfromthefactory
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. Followtheinstructionsto“TurnOffGastotheAppliance.”
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
theorificesizematchesthenameplate.NOTE:Foreleva-
tionsover2,000feet,useTable7todetermineorificesize.
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.
!

11
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. Thefirstlightingofthefurnaceafteranyhomesetup
mustbeperformedby a qualifiedservicetechnician.
b. Ifthisappliancehasapilotthatmustbelitbyhand,follow
these instructions exactly.
c. BEFORELIGHTINGsmellallaroundthefurnaceforgas.
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
notuseanyphoneinyourbuilding. Immediatelycallyour
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. Useonlyyourhandtopushinthegascontrollever. Never
usetools. Ifthe lever willnotpushinby hand,don’ttryto
repair it. Call a qualified service technician. Force or
attempted repair may result in a fire or explosion.
f. Donotusethis furnace ifanyparthasbeen under water.
Immediatelycall 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
N
A
T
N
A
T
L
P
L
P
N
A
T
N
A
T
OR
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
ORIFICESIZE-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
ORIFICESIZE-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
ORIFICESIZE-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
ORIFICESIZE-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
ORIFICESIZE-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
ORIFICESIZE-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

12
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
foundattheendofthepilottube,justleftofthepilotshield.
g. Slightlydepressthegascontrolleverandmoveitright to
the“ON”positionandrelease;thenmoveittothe“PILOT”
position.
h. Move the control lever to “SET” and hold. Immediately
lightthepilotwithamatch. Ifthisfurnaceisequippedwith
aPiezo Ignitor,activate sparklever/button several times
untilflame is visible through observationdoor. Continue
toholdthecontrolleverforaboutone(1)minuteafterthe
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
yourservicetechnicianorgassupplier.Ifthepilotwillnot
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. Turnonallelectricpowertothefurnace. Setthethermo-
statto“Heat”and/orthedesiredtemperaturesetting. 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
Afterthegaspipingtothefurnaceiscomplete,allconnections
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.
Ifthetestpressureislessthanorequalto1/2psig(14 in.
watercolumn),thefurnacemustbeisolatedfromthegas
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

13
6. ACCESSORIES
Relay Boxes
OnlytheM1GHrequiresarelaybox.AllotherM1GandM1M
furnaces are AC ready. The M1GH series furnaces are
certifiedtobeusedwitheithera4wirerelaybox(p/n902898A)
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-
mumACcapacityofyoursystem, a largerblowerwillhaveto
beinstalled. Ablowerassemblymayalsoneedtobeinstalled
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. Verycoldoutsideairtemperaturesbeingdrawninthrough
the VentilAire system.
2. Nighttimethermostatsetbacktoaverylowtemperature.
3. System is left off for extended periods of time.
Thefanmaybecyclingduringa normal call forheat. Forgas
models,makesurethegasvalveisreachinghighfire. Ifthere
arenoproblemswiththefiringrate,installaNordynefantimer
kit,partnumber903490. Seeinstructionswithkitforinstalla-
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
fromoperatingatthesametime.Thisinterlocksystemusually
containseither a“Heat-Cool” switchwhich mustbe turnedto
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
Thefurnacemustalsobeequippedwithanautomaticdamper
(See Figure 37 or 38, NORDYNE p/n 901996 for furnaces
without coil cavity, or p/n 901083 with coil cavity) to prevent
coldairfrombeingdischargeduparoundtheheatexchanger.
Coldairmaycausecondensationinsidetheheatexchanger,
which can lead to rust and early failure.
Optional Add-On Air Conditioning – Split Systems
ThereisaNORDYNEsplit-systemorpackageairconditioner
designed for your total comfort needs. Whether split system
orsinglepackage,anenergy-savingNORDYNEunitisavail-
able that has been designed specifically for manufactured
housingapplicationsandcanbesthandleyourhomecomfort
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
extensionscanbeadded—part#901937-each16”long.

14
Standing Pilot
Model M1G Furnace
Sequence of Operation
Troubleshooting
Wiring Diagrams

15
Call for heat,
t-stat closes R-W
Power On
L1 A/C Voltage
No
Yes
Yes
Power up
Selector Switch
Check incoming
power supply to
furnace and
selector switch
No
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
Yes
24 Volts at Gas Valve
Lever in ON Position
Inlet gas pressure OK
Replace Valve
Yes
Yes
14 second
second stage
high fire
No
Yes
Yes
Air Circulating
Blower Starts
No
Yes
Thermostat
Satisfies
No
No
Fan Switch
closes at 115˚ Power at
Motor
Yes
Replace
Motor
No
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˚
No
Replace
Switch
Troubleshooting Sequence – M1G 056-070

16
Call for heat,
t-stat closes R-W
Power On
L1 A/C Voltage
No
Yes
Yes
Power up
Selector Switch
Check incoming
power supply to
furnace and
selector switch
No
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
No
Pressure Switch
closes Refer to Pressure Switch section
Yes
Yes
No No
Gas valve opens
first stage, low fire Pilot lit Relight pilot
Consult Pilot Outage
section and chart
Yes
Yes
24 Volts at Gas Valve
Lever in ON Position
Inlet gas pressure OK
Replace Valve
Yes
Yes
14 second
second stage
high fire
No
Yes
Yes
Air Circulating
Blower Starts
No
Yes
Thermostat
Satisfies
No
No
Fan Switch
closes at 115˚ Power at
Motor
Yes
Replace
Motor
No
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˚
No
Replace
Switch
No
Combustion Air
Motor starts Refer to Combustion Air Blower
and Blower Relay sections
for troubleshooting
Yes
No
Refer to Low Voltage and
Limit Control sections
Troubleshooting Sequence – M1G 077-090 Combustion Blower Model

17
7. Standing Pilot Model M1G
SEQUENCE OF OPERATION FOR STANDING PILOT
a Ona call forheat, the thermostatcontacts 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. Whenthecallforheatissatisfiedthethermostatcontacts
open, the gas valve shuts off gas flow.
SEQUENCE OF OPERATION FOR STANDING PILOT W/
INDUCED DRAFT BLOWERS
a. Onacallfor heat,thethermostat contactsclose,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. Whenthecallforheatissatisfiedthethermostatcontacts
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.Ifold2-wireromexexistsitshouldbereplacedwitha
2-wirew/ground.Acoldwaterlinecouldbeusedprovidedthat
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)
AllM1Gfurnacesareprotectedbyafuseinthe24vaccircuit.
Thetransformersuppliescontrolvoltage(24vac)bystepping
down the supply (primary) voltage from 115 vac to 24 vac
(secondary voltage). All M1 transformers are rated at 30 VA.
VAisthevolt/amportotalwattagethesecondarycanhandle.
Whenatransformerisreplaced,theVA should be atleast30
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. Ifvoltageis115vacmeasurethevoltageatthesecondary
terminals marked "24 vac" & "Com" on the transformer.
4. If115vacismeasuredatprimarybutnovoltageispresent
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
powertothe furnaceonandoff. Theswitchmustbesetinthe
“On”positionforthefurnacetooperate. ForM1G*models,in
warm weather there is a possibility of the blower coming on
periodically or operating continuously due to a heat buildup
withinthefurnacebyacombinationofwarmweatherandheat
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. Ifbloweroperationisnotdesired,theOn-Offswitch
maybe set inthe“OFF” positiontocut theelectricalpower to
the furnace.
GROUND
NEUT.
HOT
OK
VOLTS AC
VOLTS DC
OHMS
MICRO
AMPS
Volts Com Prep
GROUND
NEUT.
HOT
HOTNEUTRAL
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

18
Low Voltage Wiring – Install the thermostat per the
manufacturer'sinstructions.Thelowvoltage(24vac)connec-
tionsfromthethermostataremadeattheterminalstriponthe
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.
Thethermostatmustnotbeinstalledonanoutsidewallorany
otherlocationwhereitsoperationmaybeadverselyaffected.
Adverse effects include radiant loading from fireplaces, sun-
light,orlightingfixtures,andconvectiveloadingfromwarmair
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.
OR
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
automaticreset types. Ifeither limittrips, theburner willshut
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
throughthethermostatfromthe“W”terminal.Ithasa24VAC
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
combustionair blower incorporatedinseries withtheair 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.
Uponacallforheatundernormalconditions,thecombustion
blowerstartsupandsuppliescombustionairtothechamber.
If motor does not start, check to be sure call for heat is
established. Seetroubleshootingflowchartandsequenceof
operation for further details. Then disconnect blower molex
plugand check forvoltageat plug. Ifvoltageis availableand
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,usingtheinformationfromabove,youhavedeterminedthe
combustion motor assembly needs to be replaced,use the
followingprocedure:
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
Figure15). Inletpipemayalsobreakloose,thisisnormal.
3. Remove screws from bottom of assembly and remove
the whole assembly.
4. Mountnewassembly,reattachscrewsremovedinstep3
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.
PressureSwitch– TheM1G077-090usesadifferentialtype
pressure switch. The purpose of this switch is to insure that
agoodsupplyofcombustionairissuppliedtotheburner. The
combustionblowercreatesadifferentialinnegativepressure
(lessthanatmosphericpressure)acrosstheorificering. The
switchisnormallyopenandclosesonadropinpressure,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

19
Under normal operating conditions, once the ventor motor
builds up to speed sufficient differential (negative) pressure
(approximately-0.30”wc)willbecreatedtoclosethedifferen-
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. Negativepressurecreatedbytheforceddraftmotormust
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
metershowsinfinitereading,andapressureof-.30”w.c.
orhigherispresent,switchisopen,andmustbereplaced.
Ifthepressuredifferentialreadingwillnotpulldownto-.30”
w.c., possible causes could be:
1. Restriction in air inlet pipe, this causes a greater negative
attheinletsideconnection. Thiswillacttoopenswitch. To
provethis,disconnectthehosegoingtothetopconnection.
Ifswitchcloses,thereistoomuchnegativepressurebeing
created on the inlet side. Look for air inlet restriction.
2. Ifthereisaheatexchangerrestrictionorexhaustrestriction
(anyrestrictionaftermotor),itwillcausealackofnegative
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,cleaningofpilotandburner,andinspectingthe
heat exchanger, the burner assembly must be removed.
Changing Complete Burner Assembly
1. GasLine-Removethefurnacedoorthendisconnectand
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. Becarefulnottodamageordirtytheconnector
ends.
3. MainBurnerMountingPlate-Usingaphilipsscrewdriver,
remove the screws that hold the main burner mounting
plate to the furnace.
4. BurnerAssembly-Slidetheburnerassemblyoutfromthe
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. Restrictiononoutletsideofcombustionblower(blocked
flue or debris building up in flue).
2. Leak (lack of restriction) on inlet side. Inducer inlet
leaking,inducerblowerpropslooseornotattached,or
wrong restrictor orifice.
3. To test for restriction in outlet pipe (exhaust) to verify
problem is outside of furnace, disconnect exhaust for
testperiodonlyandstartfurnace.Iffurnacestarts,look
for problem in vent pipe. Reconnect after testing.
Higher than normal negative pressure at top
connection(actstoopenswitch)maybecausedby:
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-
tionedaboveininletpipe.Note:topconnectionacts
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:

20
Gas Valve - Thegas 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.”
Asmall orificeis placedin the gaspassage todelay thebuild
upoftheworkingpressure. Aminimumoftwominutespause
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
fieldadjustable.
Testing Operating Pressure:
a. Remove furnace door and set the gas valve in the OFF
position.
b. Usinga3/16”Allenwrench,removetheplugfromtheright
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. Lightthepilotbyfollowingtheinstructionsonthefurnace
and set the gas valve switch to the ON position.
f. With the valve in the ON position, set the thermostat
aboveroomtemperaturesothefurnacewillrunthroughout
the test procedure.
g. With the furnace operating, check for valve staging. The
operatingpressureshould beapproximately3.5”WC for
Natural Gas, 10” WC for LP gas.
Pilot Assembly, Thermocouple, and Venturi Burner
Thepilotlightsthemainburner. Thethermocouplegenerates
around30MVunloaded,(unscrewedfromvalve)andaround
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,
counterclockwisetoincreaseit.Note:Donotconfusethepilot
adjustment screw with the pressure regulator, which in-
creasesbyturningclockwiseanddecreasesbyturningcoun-
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