ICP N9MP1 User manual

MULTI POSITION
SINGLE STAGE
GAS FURNACES
Part Number
440 08 2001 02
N9MP1, N9MP2 & *9MPD
“A1 & A2”
Manufactured by:
This manual supports condensing gas furnaces manufactured in 2001
ã2001 International Comfort Products Corporation (USA)
4/2002

N9MP1 -- Indoor combustion air (1 pipe only)
N9MP2 -- Direct Vent ONLY (2 pipe only)
*9MPD -- Dual Certified Venting (1 or 2 pipes)
* Denotes Brand (T, C or H)

Service Manual
Single Stage Multi Position Furnace
TABLE OF CONTENTS
1. INTRODUCTION 2............................................................
2. UNIT IDENTIFICATION 2.....................................................
3. FURNACE THEORY OF OPERATION 3........................................
4. ELECTRICAL SUPPLY 4......................................................
5. INTERLOCK SWITCH 5......................................................
6. GAS SUPPLY 5..............................................................
7. BURNERS 7................................................................
8. L.P. PRESSURE SWITCH 7...................................................
9. HIGH ALTITUDE OPERATION 7...............................................
10. CHECKING TEMPERATURE RISE 8..........................................
11. ROOM THERMOSTATS 8....................................................
12. CONTROL WIRING 9.......................................................
13. TWINNING KITS 10..........................................................
14. LIMIT SWITCHES 10.........................................................
15. PRESSURE SWITCHES 12...................................................
16. VENT/COMBUSTION AIR PIPING 14..........................................
17. STANDARD VENT TERMINATION 14..........................................
18. CONCENTRIC VENT TERMINATION 16........................................
19. EXHAUST BLOWER 17......................................................
20. CONDENSATE DRAIN TRAP 17...............................................
21. HONEYWELL ST9160B FAN TIMER/FURNACE CONTROL 18....................
22. ST9160B TESTING SEQUENCE 19............................................
23. ST9160B -- UNIQUE CONTROL FUNCTIONS/RESPONSES 19...................
24. HONEYWELL SV9541M GAS VALVE/IGNITION SYSTEM 20.....................
25. HONEYWELL SV9541M SYSTEM OPERATION 20..............................
26. CHECKING FLAME CURRENT 21.............................................
27. CAPACITORS 22............................................................
28. BLOWER ASSEMBLY 22.....................................................
29. BLOWER ROTATION 23......................................................
30. HEAT EXCHANGER REMOVAL/REPLACEMENT 44.............................
SV9541M “SMART VALVE” -- Sequence of Operation 45.............................
SV9541M “SMART VALVE” -- Trouble shooting 47...................................
SV9541M “SMART VALVE” -- Electrical Variation 49.................................
WIRING DIAGRAM 50...........................................................
TECHNICAL SERVICE DATA (N9MP1 or 2) 52......................................
TECHNICAL SERVICE DATA (*9MPD/A1) 54......................................
TECHNICAL SERVICE DATA (*9MPD/A2) 55......................................
BLOWER PERFORMANCE DATA (N9MP1 or 2 & *9MPD) 56.........................
APPENDIX OF HELPFUL INFORMATION 57.......................................

Single Stage Multi Position Furnace
Service Manual
2
440 08 2001 02
1. INTRODUCTION
This service manual is designed to be used in conjunction
with the installation manual and/or technical support manual
provided with each furnace.
These furnaces represent the very latest in high efficiency
gas furnace technology. Consequently, they incorporate the
use of certain controls that contain highly sophisticated elec-
tronic components which are not user serviceable. there-
fore, it is essential that only competent, qualified, service
personnel attempt to install, service, or maintain this prod-
uct.
This Service manual was written to assist the professional
HVAC service technician to quickly and accurately diagnose
and repair any malfunction of this product.
This service manual covers our new multi--position furnaces,
both Direct Vent (2 pipe Only), Indoor combustion (1 pipe
Only) and Dual Certified (1 or 2 pipe) models. The overall op-
eration of all of these models is essentially the same.
This manual, therefore, will deal with all subjects in a general
nature (I.E. all text will pertain to all models) unless that sub-
ject is unique to a particular model or family, in which case
it will be so indicated.
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 test instruments.
Installation or repairs made by the 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 damage 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.
!
2. UNIT IDENTIFICATION
The unit’s rating plate contains important information for the
service technician. It also lists the complete Model Manufac-
turing and Serial Numbers.
These complete numbers are required to obtain correct re-
placement parts (example, in certain model families a unit
having a MARKET REVISION of “C” is likely to be equipped
with one or more different components.
MODEL NUMBER IDENTIFICATION GUIDE
* 9 MP D075 B12 A 1
Brand Identifier Engineering Rev.
T=Tempstar Denotes minor changes
C = Comfortmaker Marketing Digit
H=Heil Denotes minor change
A = Arcoaire
X = Evaluation Cooling Airflow
Brand Identifier 08 = 800 CFM
8 = Non--Condensing, 80+% Gas Furnace 12 = 1200 CFM
9 = Condensing, 90+% Gas Furnace 14 = 1400 CFM
Installation Configuration 16 = 1600 CFM
UP = Upflow DN = Downflow UH = Upflow/Horizontal 20 = 2000 CFM
HZ = Horizontal DH = Downflow/Horizontal
MP = Multiposition, Upflow/Downflow/Horizontal Cabinet Width
Major Design Feature B = 15.5²Wide
1 = One (Single) Pipe N = Single Stage F = 19.1²Wide
2=TwoPipe P=PVCVent J = 22.8²Wide
D = 1 or 2 Pipe T = Two Stage L = 24.5²Wide
L = Low NOx V = Variable Speed Input (Nominal MBTUH)

Single Stage Multi Position Furnace Service Manual
3440 08 2001 02
Circulating Air Blower
Rating Plate
Gas Valve/Ignition Module
Door Interlock Switch
Pressure Switch
Component Locations for Four Position Furnaces
Fan/Delay Control
Furnace Vent Pipe
Combustion Air
Blower
Vent Pipe
Grommet
Primary Heat Exchanger
Secondary Heat Exchanger
Figure 1
dwg 25--23--29a
Diagnostic Light
Manual Gas Valve
Vent Drain Fitting
3/4²OD Transition Box
Drain Hose
5/8²OD Vent Pipe
Drain Hose
Plastic Transition Box
Air Intake Pipe
(Dual Certified or Direct
Vent Model)
3. FURNACE THEORY OF OPERATION
The high efficiencies and lower profile (compared to previous
series) of this furnace have been obtained using design tech-
niques not typical of traditional furnace designs. A brief de-
scription of these new design techniques and the purpose
they serve follows.
1. Reducing the height of the furnace while maintaining
the high efficiency of pervious models required main-
taining the surface area of the heat exchanger and yet
minimizing the overall size.
The design required to achieve these results is the “SER-
PENTINE” design, wherein the flue gasses must follow a
serpent shaped passage through the heat exchanger via
convection.
This “Serpentine” path is resistive to normal convective flow,
and requires that a partial vacuum be created at the outlet
of the heat exchanger to maintain the flow of flue products
through the heat exchanger.
2. The serpentine heat exchanger design does not lend
itself well to the ribbon type, or slotted port type burner
found in more traditional design furnaces for the follow-
ing reasons:
A. The secondary combustion airflows at right angles
to the burner flame, making it likely to “pull” the flame
off a ribbon or slotted port type burner.
B. The flame “height” of a ribbon or slotted port type
burner would make it difficult (if not impossible) to
prevent impingement of the flame on the heat ex-
changer surfaces whole maintaining the low profile
heat exchanger.
For these reasons, an “INSHOT” type burner is used in this
series. The inshot burner (also called a “jet” burner) fires a
flame straight out its end. This burner is designed to fire into
a tube style heat exchanger, making it an ideal application in
the tube--like passages of the serpentine heat exchanger.
3. In order to extract the maximum amount of heat pos-
sible from the flue gasses, a secondary heat exchang-
er (condenser) is connected to the outlet of the primary
heat exchanger. This condenser removes additional
heat from the flue gasses, causing their temperature to
drop below dew point. This results in the forming of
condensation (water) which then must be routed to a
drain.
4. The placement of the secondary heat exchanger at the
outlet of the primary heat exchanger creates additional
resistance to the flow of gasses.
5. To overcome the resistance to convective flow of the
Primary and Secondary heat exchangers requires the
use of an Induced Draft Combustion Blower Assembly.

Single Stage Multi Position Furnace
Service Manual
4
440 08 2001 02
6. The Combustion Blower Assembly is mounted on the
outlet side of the Secondary heat exchanger, This
blower creates a partial vacuum (negative pressure)
within the heat exchangers drawing the flue products
out of the furnace.
7. A pressure switch (Air Proving Switch) is used as a
safety device that prevents the ignition system from fir-
ing the furnace until it senses that a proper draft has
been established through the furnace.
4. ELECTRICAL SUPPLY
Electrical shock hazard.
Turn OFF electric power at fuse box or service panel
before making any electrical connections and en-
sure a proper ground connection is made before
connecting line voltage.
Failure to do so can result in death, personal injury
and/or property damage.
!
SUPPLY CIRCUIT
The furnace cannot be expected to operate correctly unless
it is properly connected (wired) to an adequately sized (15
amp.) single branch circuit.
SUPPLY VOLTAGE
Supply voltage to the furnace should be a nominal 115 volts.
It MUST be between 97 volts and 132 volts. Supply voltage
to the furnace should be checked WITH THE FURNACE IN
OPERATION. Voltage readings outside the specified range
can be expected to cause operating problems. Their cause
MUST be investigated and corrected.
ELECTRICAL GROUND
Grounding of the electrical supply to ALL FURNACES IS
REQUIRED for safety reasons.
CHECKING GROUNDING AND POLARITY
Grounding may be verified as follows:
1. Turn the power supply “OFF”.
2. Using an Ohmmeter check for continuity between the
Neutral (white) wire and Ground wire (green) of the
supply circuit.
3. With the Ohmmeter set on the R x 1 scale, the reading
should be zero Ohms.
4. A zero Ohm reading indicates that the neutral is
grounded back to the main panel.
5. An alternate check would be to check for continuity
from the Neutral to a cold water pipe, (Pipe must be
metal, and must have a continuous, uninterrupted con-
nection to ground) or to a continuous, uninterrupted
connection to ground) or to a driven ground rod.
6. Any readings other than zero Ohms would indicate a
poor ground, or no ground.
Polarity may be verified as follows:
1. Turn the power supply “ON”.
2. Using a Voltmeter check for voltage between the Hot
(Black) and Neutral (White) wire of supply circuit.
POLARITY
CORRECT POLARITY of the line voltage supply to all fur-
naces is also required for safety reasons.
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. A zero Volt reading indicates there is no voltage poten-
tial on Neutral wire.
7. Double check by checking for voltage between the Hot
(Black) wire and Ground wire of the supply circuit.
8. Reading should be Line (supply) Voltage.(ifzero
volts is read, there is no ground, or polarity is re-
versed.)
Figure 2 Electrical Connections
NOTE: Junction Box can
be mounted to either the
left or right side.
25--23--42

Single Stage Multi Position Furnace Service Manual
5440 08 2001 02
5. INTERLOCK SWITCH
The blower compartment door of all models is equipped with
an interlock switch. This switch is “Normally Open” (closes
when the door is on the furnace) and interrupts furnace op-
eration when the door is open. This interlock switch is a safe-
ty device, and SHOULD NEVER BE BY--PASSED.
Since this is a single pole switch, (breaking only one side of
the line) proper line voltage is essential to insure that furnace
components are not “HOT” when switch is open. (See
Checking Grounding and Polarity)
Figure 3 Typical Interlock Switch
10--12--96
6. GAS SUPPLY
Typical Gas Valve HoneywellFigure 4
dwg 25--23--31a
INLET
Manifold Pressure
Adjustment
Pilot Pressure
Adjustment (Hid-
den)
On\Off
Switch
Diagnostic Light
OUTLET
An adequately sized gas supply to the furnace is required for
proper operation. Gas piping which is undersized will not
provide sufficient capacity for proper operation. Piping
should be sized in accordance with accepted industry stan-
dards.
NATURAL GAS
Inlet (Supply) pressure to the furnace should be checked (at
the gas valve) with ALL OTHER GAS FIRED APPLIANCES
OPERATING. Inlet (Supply) pressure to the furnace under
these conditions MUST be a minimum of 4.5²W.C. (Water
Column). If the inlet pressure is less, it may be an indication
of undersized piping or regulator problems.
L.P. GAS
Inlet (Supply) pressure to the furnace should be checked in
the same manner as for Natural Gas, however with L.P. Gas,
the inlet pressure MUST be a minimum of 11²W.C. If this
cannot be obtained, problems are indicated in either the reg-
ulator or pipe sizing.
Table 1 Gas Pressures Below 2000¢
¢¢
¢
Gas
T
Supply Pressure Manifold
P
Type Recommended Max. Min. Pressure
Natural 7²14²4.5²3.5²
LP 11²14²11²10²
Important Note:
·With Propane gas, the rated input is obtained when the
BTU content is 2,500 BTU per cubic foot and manifold
pressure set at 10²
²²
²W.C.
·If Propane gas has a different BTU content, orifices
MUST be changed by licensed Propane installer.
·Measured input can NOT exceed rated input.
·Any major change in gas flow requires changing burner
orifice size.
CHECKING INPUT (FIRING) RATE
Once it has been determined that the gas supply is correct
to the furnace, it is necessary to check the input (firing) rate,
This can be done in two (2) ways. First by checking and ad-
justing (as necessary) the manifold (Outlet) pressure. The
second way is to “Clock” the gas meter.
Fire or explosion hazard.
Turn OFF gas at shut off before connecting
manometer.
Failure to turn OFF gas at shut off before
connecting manometer can result in death,
personal injury and/or property damage.
!

Single Stage Multi Position Furnace
Service Manual
6
440 08 2001 02
Gas Pressure Testing Devices
Figure 5
MAGNEHELIC
MAX. PRESSURE 15 PSIG
0
510
15
INCHES OF WATER
Pressure Connections
Typical "U" Tube
Manometer
0
1
1
2
2
3
3
CHECKING MANIFOLD PRESSURE
1. Connect a manometer or Magnehelic gauge (0--12²
W.C. range) to the pressure tap on the “OUTLET” side
of the gas valve.
2. Turn gas “ON”, fire the furnace, and remove adjust-
ment cover (screw--cap).
3. Turn adjustment screw clockwise (IN) to INCREASE
pressure, and counterclockwise (OUT) to DECREASE
pressure.
4. At altitudes BELOW 2,000¢
¢¢
¢set manifold pressure to
3.5²W.C. for Natural Gas, and 10²W.C. for L.P. Gas.
5. For Natural Gas units ABOVE 2,000¢
¢¢
¢, set manifold
pressure according to TABLE 2.
6. For L.P. Gas units ABOVE 2,000¢
¢¢
¢, insure that orifice
size has been changed (per “National Fuel Gas Code”
-- Appendix “F”) if gas supply has not already been de--
rated for altitude by the gas supplier.
7. For ALL UNITS ABOVE 8,000¢, contact the factory for
SPECIFIC de--rating information.
MANIFOLD PRESSURE AND ORIFICE SIZE FOR HIGH ALTITUDE APPLICATIONS
Table 2 NATURAL GAS
H
e
a
t
V
a
l
u
e
Elevation Above Sea Level
H
eat
V
a
l
ue
Btu/Cu.Ft. 0--1999
(²
²²
²×
××
×wc)
2000--2999
(²
²²
²×
××
×wc)
3000--3999
(²
²²
²×
××
×wc)
4000--4999
(²
²²
²×
××
×wc)
5000--5999
(²
²²
²×
××
×wc)
6000--6999
(²
²²
²×
××
×wc)
7000--7999
(²
²²
²×
××
×wc)
800 3.5 3.5 3.5 3.5 3.5 3.5 3.5
850 3.5 3.5 3.5 3.5 3.5 3.5 3.5
900 3.5 3.5 3.5 3.5 3.5 3.5 3.4
950 3.5 3.5 3.5 3.5 3.3 3.2 3.1
1000 3.5 3.4 3.3 3.2 3.0 2.9 2.8
1050 3.2 3.1 3.0 2.9 2.7 2.6 2.5
1100 2.9 2.8 2.7 2.6 2.5 2.4 2.3
Orifice Size #42 #42 #42 #42 #42 #42 #42
“CLOCKING” GAS METER (NATURAL GAS)
1. Check with gas supplier to obtain ACTUAL BTU con-
tent of gas.
2. Turn “OFF” gas supply to ALL other gas appliances.
3. Time how many seconds it takes the smallest (normal-
ly 1 cfh) dial on the gas meter to make one complete
revolution.
4. Calculate input rate by using ACTUAL BTU content of
gas in formula shown in example.
Example
Natural Gas
BTU Content
No. of Seconds
Per Hour
Time Per Cubic
Foot in Seconds
BTU Per
Hour
1,000 3,600 48 75,000
1,000 x 3,600 ¸48 = 75,000 BTUH

Single Stage Multi Position Furnace Service Manual
7440 08 2001 02
7. BURNERS
Burners used in this series of furnace are of the “INSHOT”
type. Their operation can be compared to that of a torch in
that they produce a hard, sharp, somewhat noisy flame.
Noise should not be an issue, however, because of the
closed compartment design. In order to insure that the burn-
ers are operating properly, and at their design noise level,
proper adjustment of the gas (manifold) pressure is essen-
tial. See page 6 for further information on manifold pressure
adjustments.
The burners used in this series ARE NOT EQUIPPED WITH
AIR SHUTTERS, as none are required. Proper operation
(flame characteristics) is obtained by insuring that the orifice
size, and manifold pressure are correct for the fuel being
used and the altitude of the installation.
Main Burner
Burner Face
10--10--78
Figure 6
8. L.P. PRESSURE SWITCH
Models converted to operate on L.P. Gas will be installed
with an L.P. Pressure Switch. If so equipped, the switch will
be located in the gas supply line (in a “Tee” fitting), just ahead
of the gas valve.
The purpose of this switch is to prevent furnace operating un-
der low line (Supply) pressure conditions. Operating under
low line pressure conditions, can create problems such as in-
complete combustion, flashback, sooting, etc.
The switch is a “Normally Open” pressure operated switch
that is wired in series with the furnace (vent) pressure switch.
The L.P. Pressure Switch closes when line (Supply) pres-
sure is 8.0²W.C. or higher. the L.P. Pressure Switch Opens
if line pressure falls below 6.0²+0.6²W.C. interrupting
power to the gas valve.
On some models, it is located (electrically) between the Fur-
nace (vent) pressure switch and the gas Valve.
Typical L.P. Pressure Switch
Figure 7
9. HIGH ALTITUDE OPERATION
These furnaces are designed to operate in the majority of the
country without modifications. At altitudes over 2,000¢above
sea level, however, certain measures need to be taken to in-
sure continued, safe reliable operation. For example, units
must be de--rated for altitude (by adjusting manifold pres-
sure and/or changing orifice size) based upon the type of fuel
(I.E. Natural Gas or L.P. gas), Btu content of the gas, and
installed altitude.
ALL UNITS must have a high altitude pressure switch
installed at altitudes above 4,000¢above sea level.
When servicing a unit installed at altitudes above 2,000¢in-
sure that it has been properly modified to operate at that alti-
tude. See the sections on Gas pressure (Page *), and pres-
sure switches (Page **) to obtain specific information for you
particular installation altitude.

Single Stage Multi Position Furnace
Service Manual
8
440 08 2001 02
10. CHECKING TEMPERATURE RISE
Checking Temperature Rise
Figure 8
Thermometer:
Return Air Temp.
Thermometer;
Supply Air Temp.
Supply
Air Flow
Air Flow
Return
The furnace is designed to operate within a certain specified
range of temperature rise.
Operating the furnace outside the specified range may result
in lower efficiency and/or comfort levels, as well as prema-
ture combustion component failures.
Simply stated, the temperature rise through the furnace is
the difference in temperature between the return air, and the
supply air.
NOTE: BEFORE CHECKING TEMPERATURE RISE BE
CERTAIN THAT MANIFOLD PRESSURE IS PROPERLY
ADJUSTED.
ALLOWABLE TEMPERATURE RISE ALL
MODELS
Model Range
50 Mbtu 35°F--65°F
75, 100 & 125 Mbtu 40°F--70°F
Operate the furnace for 15 minutes before taking tempera-
ture readings. Subtract the return air temperature from the
supply air temperature. The result is the temperature rise.
Compare with the allowable rise listed for the model (size)
you are checking.
Temperature Rise can be checked by placing a thermometer
in the return air duct within 6¢of furnace. Place a second ther-
mometer in the supply duct at lease two (2) ft. away from the
furnace. (This will prevent any false readings caused by radi-
ation from the furnace heat exchanger) Make sure that the
FILTER IS CLEAN and that ALL REGISTERS AND/OR
DAMPERS ARE OPEN.
If the rise is not within the specified range, it will be necessary
to change the heating blower speed. If the rise is too high,
it will be necessary to increase the blower speed.If the
rise is too low, it will be necessary to reduce the blower
speed.
Example:
Supply Temp. 170°
Return Temp. 70°
Temperature Rise 100°=
Too High
Solution: Increase Blower Speed
11. ROOM THERMOSTATS
Room thermostats are available from several different
manufactures in a wide variety of styles. They range from the
very simple and inexpensive Bi--metallic type to the complex.
They are simply a switch (or series of switches) designed to
turn equipment (or components) “ON” or “OFF” at the de-
sired conditions.
An improperly operating, or poorly located room thermostat
can be the source of perceived equipment problems. A care-
ful check of the thermostat and wiring must be made then to
insure that it is not the source of problems.
Thermostat Location
Figure 9
5 ft.
DRAFTS
SUN
THERMOSTAT
LIGHT
SHIELD

Single Stage Multi Position Furnace Service Manual
9440 08 2001 02
LOCATION
The thermostat should not be mounted where it may be af-
fected by drafts, discharge air from registers (hot or cold), or
heat radiated from the sun of appliances. Never install in al-
coves, bathrooms or bedrooms.
The thermostat should be located about 5 ft. above the floor
in an area of average temperature, with good air circulation.
Normally, an area in close proximity to the return air grille is
the best choice.
Mercury bulb type thermostats MUST be level to control tem-
perature accurately to the desired set--point. Electronic digi-
tal type thermostats SHOULD be level for aesthetics.
HEAT ANTICIPATORS
Heat anticipators are small resistance heaters built into most
electric--mechanical thermostats. Their purpose is to pre-
vent wide swings in room temperature during furnace opera-
tion.
In order to accomplish this, the heat output from the anticipa-
tor must be the same regardless of the current flowing
through it. Consequently, most thermostats have an adjust-
ment to compensate for varying current draw in the thermo-
stat circuit.
The proper setting of heat anticipators then is important to
insure proper temperature control and customer satisfac-
tion.
Measuring Current Draw
Figure 10
Ammeter
W
R
Subbase
Amps
The best method to obtain the required setting for the heat
anticipator, is to measure the actual current draw in the con-
trol circuit (“W”) using a low range (0--2.0 Amps) Ammeter.
(See Figure 10) After measuring the current draw, simply
set the heat anticipator to match that value.
If a low range ammeter is not available, a “Clamp--on” type
meter may be used as follows:
1. Wrap EXACTLY ten (10) turns of wire around the jaws
of a clamp--on type ammeter.
2. Connect one end of the wire to the “W” terminal of the
thermostat sub--base, and the other to the “R” termi-
nal.
3. Turn power on, and wait approximately 1 minute, then
read meter.
4. Divide meter reading by 10 to obtain correct anticipator
setting.
If an ammeter is not available, a setting of 0.30 amps may
be used for models equipped with the HONEYWELL
SV9541M Gas Valve/Ignition Control. They should, howev-
er, provide satisfactory operation in most cases.
Electronic thermostats do not use a resistance type anticipa-
tor. These thermostats use a microprocessor (computer)
that determines a cycle rate based on a program loaded into
it at the factory.
These cycle rates are normally field adjustable for different
types to equipment. The method of adjustment, however,
varies from one thermostat manufacturer to another. Check
with the thermostat manufacturer to find out the proper way
of adjusting the cycle rate.
12. CONTROL WIRING
Control wiring is an important part of the total equipment
installation, since it provides the vital communications link
between the thermostat, and the equipment malfunctions.
Control wiring that is either too long, undersized, or improp-
erly connected (be it simply loose, or on the wrong terminal)
can in fact be the source of many equipment problems.
ALWAYS check to make sure that the control wiring is con-
nected to the proper terminal(s) of the equipment and ther-
mostat you are using. Remember, also, that the thermostat
terminals are not always identified alike by different thermo-
stat manufacturers. Connections MUST be clean and tight
to insure trouble--free operation.
For years, installers have run a wire from the “Y” terminal of
the room thermostat and connected it directly to the contact
on coil of a condensing unit. (not making any connection to
the furnace with this wiring. Then, run the low voltage “Com-
mon” wire from the condensing unit back to the “C” terminal
of the furnace.
With the HONEYWELL ST9160B electronic Fan Timer/Fur-
nace Control, the “Y” terminal of the furnace does in fact
serve a particular purpose. Failure to connect it will result in
certain improper operation as follows:

Single Stage Multi Position Furnace
Service Manual
10
440 08 2001 02
The COOLING fan speed is energized via the “Y” terminal.
Failure to connect the thermostat “Y” terminal to the “Y” ter-
minal on the control will result in the failure to energize the
COOLING speed on a call for cooling from the thermostat.
(The HEATING speed will be energized instead via the “G”
terminal)
13. TWINNING KITS
Some installations may require a Heating capacity or Airflow
capabilities greater than a single furnace of this series can
provide.. When this is necessary, furnaces may be installed
in a “Twinned” configuration.
The Twinning Kit allows the two (2) furnaces to be controlled
by the same room thermostat. When Twinned, the circulat-
ing (conditioned air) blowers of BOTH furnaces will operate
simultaneously.
Models equipped with a HONEYWELL ST9160B series Fan
Timer/Furnace Control may be twinned using a model
NAHA003WK01 twinning kit.
To assist troubleshooting efforts of “Twinned” installations,
“TYPICAL” control wiring diagrams are provided on pages **
through **.
14. LIMIT SWITCHES
Two (2) different kinds of limit switches are used on this se-
ries of furnaces. They are the main limit and roll out limit
switches. The main limit, and roll limit switches are used on
all models.
NOTE: All limit switches are safety devices and other
than for testing purposes, should never be jumped out!
Limit switches are “normally closed” electrical switches, de-
signed to open when their predetermined “limit setting” has
been reached.
It should also be remembered, that when a limit switch
opens, it more than likely is not due to a bad switch! The
cause of the opening limit must be found and corrected, be-
fore the furnace can resume proper operation.
Fire hazard.
Limit controls are factory preset and MUST NOT be
adjusted. Use ONLY manufacturer’s authorized
replacement parts.
Failure to do so can result in death, personal injury
and/or property damage.
!
The specific functions of the two (2) limit switches used in
this series of furnaces are as follows:
MAIN LIMIT SWITCH
A “Normally Closed” switch located on the front partition of
the furnace. It monitors supply air temperature, and inter-
rupts furnace (burner) operation when a supply air tempera-
ture is sensed which would result in the furnace exceeding
Maximum allowable outlet air temperature. While the main
limit is open, combustion blower, and/or the circulating blow-
er will be energized continuously. This control is an “Auto-
matic” reset control, which will reset itself when the tempera-
ture sensed drops to a safe level.
If furnace (burner) cycles on this limit switch, (I.E. switch
opens and closes during furnace operation) it is more than
likely due to a high temperature rise through the furnace.
(See checking temperature on page 8 of this manual)
High temperature rise can be caused by either OVER
FIRING (high manifold pressure. incorrect orifices, etc.) or
LOW AIR FLOW (dirty filter, blower speed too low, excessive
static in duct system, etc.)
Typical Limit Switch
Figure 11

Single Stage Multi Position Furnace Service Manual
11 440 08 2001 02
To verify this, the cut--out (opening) point of the switch should
be checked (using a thermocouple type thermometer con-
nected to the face of the switch) as follows:
1. Operate furnace for several minutes.
2. Block return air grille(s) to furnace.
3. Observe temperature at which switch opens (burner
operation ceases).
4. Remove blockage from return grille(s).
5. Observe temperature at which switch closes (burner
operation resumes).
6. Compare readings with the limit setting listed in the
appropriate chart for the model you are servicing.
If switch is opening within the specified range, then it is sim-
ply doing its job, and the cause of the over--temperature must
be determined and corrected.
If, however, the switch is found to be opening prematurely,
then it should be replaced. When replacing ANY limit switch,
use ONLY a switch of EXACTLY the same temperature set-
ting. Use of a different temperature limit switch can create a
dangerous situation. Some of the main limit switches used
in this series are SIMILAR IN APPEARANCE. DIFFERENT
TEMPERATURE SETTINGS, HOWEVER, ARE USED for
different models. Be certain you have the correct control for
the model you are servicing.
ROLL OUT LIMIT
A “Normally Closed” switch (wired in series with the Main
Limit switch) mounted on the burner box.
This switch may be of the manual type, depending upon the
particular model and/or family. Different temperature
(OPENING) settings are also used on different models.
When replacing this switch, be absolutely certain the correct
one is used.
Typical Roll Out Limit Switch
Figure 12
CAUTION
NEVER use an automatic reset roll out switch to replace
a manual reset type roll out switch.
Doing so may cause potentially unsafe and/or intermit-
tent operation.
The roll out switch monitors the temperature inside the burn-
er box, and interrupts furnace (burner) operation when its
temperature indicates flame roll out has occurred.
If the roll out switch has opened, the cause must be deter-
mined. Some possible reasons for flame roll out include a re-
stricted primary or secondary heat exchanger or over fired
furnace.
MANUAL RESET SWITCH MODELS
Furnace models which are equipped with a Honeywell
ST9160 Fan timer/furnace control use a manual reset roll out
switch. Once the roll out switch has opened, burner opera-
tion will be prevented until the roll out switch is “Manually Re-
set” by pressing the red button located on the switch. While
the roll out switch is open, (Depending upon the particular
model) the combustion blower and/or circulating blower will
be energized continuously.
AUXILIARY LIMIT SWITCHES
All models are equipped with one (1) additional (AUXILIARY)
limit switch mounted on the blower deck. Its purpose is to
monitor return air temperature, and interrupt burner opera-
tion when a temperature is sensed which could result in the
filter surface(s) exceeding allowable temperatures. Depend-
ing upon the particular model, the combustion blower, and/or
circulating blower may be energized continuously while the
auxiliary limit switch remains open.
This control is an “Automatic” reset control which will reset
itself when the temperature drops to a safe level. See the
Tech. Service Data Sheet for the model you are servicing, to
obtain its specific auxiliary limit switch setting.

Single Stage Multi Position Furnace
Service Manual
12
440 08 2001 02
15. PRESSURE SWITCHES
Transition Pressure Switch
This switch is designed to monitor a blockage of the conden-
sate drain line. It uses a single tap (port) “Normally Open”
pressure switch (wired in series with the furnace air proving
(pressure) switch. The switch “Closes” at a (negative) pres-
sure setting for the switch associated with that particular
model furnace (See unit specitications).
Under normal operating conditions, sufficient pressure is de-
veloped by the exhaust (combustion) blower to close the
switch, and permit the burner to operate. As the condensate
drain begins to back--up, however, the pressure begins to re-
duce. When the pressure drops sufficiently, burner operation
will be prevented until the condition is corrected.
Blower Pressure Switch
An air proving switch (pressure switch) is used on all models
to insure that a draft has been established through the heat
exchanger before allowing burner operation.
To insure continued SAFE, RELIABLE, operation, NEVER
SUBSTITUTE a pressure switch with one that is similar in
appearance. ONLY FACTORY PROVIDED or
AUTHORIZED SUBSTITUTES ARE ACCEPTABLE.
All models installed at altitudes of 4,000¢above sea level or
higher require replacing the standard pressure switch with a
high altitude pressure switch. The different pressure switch
settings allow continued SAFE, RELIABLE, high altitude
operation.
Pressure Switches
Figure 13
25--23--72
Transition
Blower
HIGH ALTITUDE PRESSURE SWITCHES - ALL
MODELS
Model Max.
Close Open Part #
Upflow
1
4
0
²
W
C
--
1
1
8
+
0
1
0
²
W
C
Downflow --1.40
²
W
.
C
.--
1
.
1
8
+
0
.
1
0
W
.
C
.
--
CHECK CURRENT TECHNICAL SUPPORT MANUAL
FOR PART NOS.
Under normal operating conditions, sufficient negative pres-
sure will be created to close the pressure switch, and keep
it closed to keep furnace operating. Under abnormal condi-
tions, however, such as a restricted vent pipe, or a leak in one
of the heat exchangers, sufficient negative pressure will not
be created. This will result in the switch failing to close or fail-
ing to remain closed during furnace operation.
When servicing a unit whose pressure switch will not close,
or remain closed during operation, the operating pressure of
that furnace should be checked and compared to
approximate operating pressures listed in Table 3 and the
switch setting(s) listed above for the model family you are
servicing.
It is important to remember, that greater negative pressures
are created by the furnace when “HOT” (I.E. upon initial
start--up) than when “COLD” (I.E. after furnaces has been in
operation for a few minutes). Because of this, furnace pres-
sure should ONLY be checked when “HOT” to insure accu-
rate readings.
Table 3 lists approximate operating pressures for Direct
Vent (I.E. Two Pipe) installations of models in this series.
They were obtained in a test lab, under controlled conditions
using two (2) specific vent lengths. They are included in this
manual to provide you with a “Barometer” to gauge our pres-
sures against. The pressures you obtain in the field will differ
slightly from these figures based upon vent length, gas pres-
sure, operating temperature, etc.
Major discrepancies in pressures, will normally cause
problems with pressure switch operation. These Major dis-
crepancies should be investigated as follows:

Single Stage Multi Position Furnace Service Manual
13 440 08 2001 02
Table 3 APPROXIMATE OPERATING PRESSURES (²
²²
²OF W.C.)
Model Vent Length @Blower @ Transition
5
0
M
b
t
u
Short -- (5¢No. Elbows) --1.80 --2.60
5
0
M
b
tu Long -- (40¢+590°Elbows) --1.30 --2.30
7
5
M
b
t
u
Short -- (5¢No. Elbows) --1.80 --2.60
75
M
b
tu Long -- (40¢+590°Elbows) --1.30 --2.30
1
0
0
M
b
t
u
Short -- (5¢No. Elbows) --1.80 --2.60
1
0
0
M
b
tu Long -- (40¢+590°Elbows) --1.70 --2.50
1
2
5
M
b
t
u
Short -- (5¢No. Elbows) --1.80 --2.60
1
2
5
M
b
tu Long -- (40¢+590°Elbows) --1.70 --2.50
Lower (Lesser) Negative Pressures
Lower than normal negative pressures measured at the
Combustion Blower may be caused by:
1. Restriction on the Outlet side of the combustion blow-
er. (I.E. Blocked Flue, Vent too long, Heat Exchanger
leak, etc.)
2. Leak (lack of restriction) on the Inlet side of the com-
bustion blower.
Higher (Greater) Negative Pressures
Higher than normal negative pressures measured at the
Combustion Blower may be caused by:
1. Restriction on the Inlet side of the combustion blower.
(I.E. Plugged Heat Exchanger, air inlet orifice too
small)
Inlet Pipe
(not used on
Single Pipe
models)
Vent Pipes MUST be
supported Horizontal-
ly and Vertically
*8²
²²
²Min.
20¢
¢¢
¢Max.
in same
atmospheric zone
Figure 14
*8²
²²
²Min.
20¢
¢¢
¢Max.
in same atmospheric zone
Coupling on ends of ex-
haust pipe. Total pipe &
coupling outside struc-
ture = 8²
²²
²
Typical Vent/Combustion Air Piping Installation
Aluminum or non--rusting shield recommended.
(See Vent Termination Shielding for dimensions).
*Increase minimum from 8²
²²
²to 18²
²²
²for cold climates (sustained temperatures below
0°
°°
°F).
DISCHARGE AIR
25--23--33
Inlet Pipe
(not used
on
Single Pipe
models)
UPFLOW
*8²
²²
²Min.
20¢
¢¢
¢Max.
in same
atmospheric
zone
Vent Pipes MUST
be supported
Horizontally and
Vertically
*Increase minimum from 8²
²²
²to 18²
²²
²for cold climates (sustained temperatures
below 0°
°°
°F).
See Vent Termination Shielding
in Vent Section.
*8²
²²
²Min.
20¢
¢¢
¢Max.
in same
atmospheric zone
8²Min.
Coupling on inside
and outside of wall to
restrain vent pipe
25--23--33a
DOWNFLOW

Single Stage Multi Position Furnace
Service Manual
14
440 08 2001 02
16. VENT/COMBUSTION AIR PIPING
Vent and combustion air piping are an extremely important
part of the total furnace installation. Improperly installed or
inadequately sized vent and/or combustion air piping can be
the source of many perceived furnace problems.
For example, most problems associated with pressure
switch operation can normally be traced to short comings in
the vent and/or combustion air piping. Anytime these type
problems arise, a thorough inspection of the vent and/or
combustion air piping should be conducted.
ALL MODELS require a vent (exhaust) pipe to carry flue
products to the outside of the structure.
Direct VENT (ONLY) models require a combustion air inlet
to bring in all air for combustion from outside the struc-
ture.
DUAL CERTIFIED models require a combustion air inlet
pipe to bring in all air for combustion from outside the struc-
ture only when installed as a Direct Vent Furnace (I.E. Two
Pipe Installation)
Consult the appropriate Venting tables and/or piping chart
for the model (series) you are servicing.
17. STANDARD VENT TERMINATION
Vent/Combustion Air Piping Charts
Dual Certified Models ONLY - Non- Direct Vent
Installation
Single Piping Chart
Table 4 Pipe Diameter Table
Single Piping ONLY
50,000 & 75,000 Btuh Furnaces
40¢& (5) 90°elbows with 2²PVC pipe or
70¢& (5) 90°elbows with 3²PVC pipe or
100,000 Btuh Furnace
70¢& (5) 90°elbows with 3²PVC pipe
125,000 Btuh Furnace
40¢& (5) 90°elbows with 3²PVC pipe
Elbows are DWV Long Radius Type for 2²and
3²vents.
If more than five elbows are required, reduce the length of both
the inlet and exhaust pipes 5¢for each additional elbow used.
NOTE: It is allowable to use larger diameter pipe and fitting than
shown in the tables but not smaller diameters than shown.
All Series (Models) - Direct Vent Installation
Dual Piping Chart
Table 5 Pipe Diameter Table
Dual Piping ONLY
50,000 & 75,000 Btuh Furnaces
40¢& (5) 90°elbows with 2²PVC pipe or
70¢& (5) 90°elbows with 3²PVC pipe or
100,000 Btuh Furnace
70¢& (5) 90°elbows with 3²PVC pipe
125,000 Btuh Furnace
40¢& (5) 90°elbows with 3²PVC pipe
Elbows are DWV Long Radius Type for 2²and
3²vents.
If more than five elbows are required, reduce the length of both
the inlet and exhaust pipes 5¢(1.5m) for each additional elbow
used.
*Feet of pipe is whichever pipe run is the longest,either inlet or
outlet side.
Figure 15 Standard Termination
Rooftop Termination
25--00--06
A
A
B
A=12²Above roof or snow accumulation level
B=8²Min., 20¢Maximum, except in areas with extreme cold
temperatures (sustained below 0°F), the 18²Min.
Inlet is optional on
Dual Certified models
Inlet is optional on
Dual Certified models
Figure 16 Sidewall Termination12²or More
Above Snow Level or Grade Level
8²
²²
²*
MIN.
20’
MAX
*18²Minimum for cold climates
(substained below 0°F)
25--00--05F

Single Stage Multi Position Furnace Service Manual
15 440 08 2001 02
Figure 17 Concentric Vent and Combustion-
Air Roof Termination
“A”
Combustion
Air
Exhaust
12²
²²
²Min.
Grade or
Snow Level
Dimension “A” is touching or 2²maximum separation.
Figure 18 Concentric Vent and Combustion--
Air Sidewall Termination
“A”
Vent
Dimension “A” is touching or 2²maximum separation.
25--22--02d
Vent
Combustion
Air
1²
²²
²Maximum
(TYP.)
Exhaust
“A”
“A”
Inlet
Figure 19 Sidewall Inlet Vent and Exhaust--Air
Termination
Dimension “A” is touching or 2²maximum separation.
12²
²²
²Min. Grade
or Snow Level
18²
²²
²Min. for
Cold Climates
(Sustained Below 0°
°°
°F)
8²
²²
²Min.
20¢
¢¢
¢Max.
8²
²²
²
Min.
Ex-
haust
Exhaust
8²
²²
²
Min.
8²
²²
²Min.
20¢
¢¢
¢Max.
Figure 20 Sidewall Inlet Vent and Exhaust--Air
Termination with Exterior Risers
Dimension “A” is touching or 2²maximum separation.
12²
²²
²Min.
Grade or
Snow Level
18²
²²
²Min. for Cold Climates
(Sustained Below 0°
°°
°F)
Inlet
“A”
“A”
12²
²²
²Min.
Grade or
Snow Level
Exhaust
8²
²²
²Min.
20¢
¢¢
¢Max.
Figure 21 Rooftop Inlet Vent and Exhaust--Air
Termination
25--22--43
18²
²²
²Min. for Cold Climates
(Sustained Below 0°
°°
°F)
Inlet

Single Stage Multi Position Furnace
Service Manual
16
440 08 2001 02
Figure 22 Recommended Alternate Installa-
tion for Sustained Cold Weather
(--0°
°°
°F & below)
OVERHANG
12²
²²
²MIN.
12²MIN. Ground
Level
OR Snow Level
INLET
EXHAUST
90°
°°
°
Same Joist
Space
FRONT VIEW SIDE VIEW
25--23--73
12²
18. CONCENTRIC VENT TERMINATION
Vent/Combustion Air Piping Charts
Table 6
Concentric Termination Kit NAHA001CV
& NAHA002VC Venting Table Dual Piping
ONLY
50,000 & 75,000 Btuh Furnaces
NAHA002CV -- 35¢& (4) 90°elbows with 2²PVC pipe
NAHA001CV -- 65¢& (4) 90°elbows with 3²PVC pipe
100,000 Btuh Furnace
NAHA001CV -- 65¢& (4) 90°elbows with 3²PVC pipe
125,000 Btuh Furnace
NAHA001CV -- 35¢& (4) 90°elbows with 3²PVC pipe
1. Do not include the field supplied 45°elbow in the total
elbow count.
2. If more than four elbows are required, reduce the length of
both the inlet and the exhaust pipes five feet for each
additional elbow used.
3. Elbows are DWV long radius type for 2²and 3²vents.
Concentric Vent Roof Installation
Figure 23
Maintain 12²min. clearance
above highest anticipated
snow level. Max. of 24²above
roof.
Combustion Air
Roof Boot/
Flashing
(Field Supplied)
Combustion
Air
Vent
Vent
Support
(Field Supplied)
45°Elbow
(Field Supplied)
25--22--02
Note:
Support must be field installed to secure termination kit to structure.

Single Stage Multi Position Furnace Service Manual
17 440 08 2001 02
Combustion
Air
Vent
Combustion
Air
Figure 24 Concentric Vent Sidewall
Attachment
3²x2²Bushings or
3²x2
1/2²Bushings
If 3²vent not used
(Field supplied)
Vent
45°Elbow
(Field Supplied)
25--22--02
Strap
(Field Supplied)
Flush to
1²max.
Note:
Securing strap must be field installed to prevent movement of termination kit
in side wall.
19. EXHAUST BLOWER
Figure 25 Exhaust Blower
11²
²²
²Section PVC pipe
Rubber Coupling
&Clamps
90°
°°
°Street
Elbow Combustion
Blower
Vent Fitting
&Clamps
25--23--35
DRAIN SIDE VIEW
Rotate downward
20°
°°
°to 30°
°°
°
Vent Pipe
(Side Panel EXit)
Vent Pipe
(Top Panel Exit)
20. CONDENSATE DRAIN TRAP
The removal of additional heat from the flue products which
takes place in the secondary heat exchanger (condenser)
causes them to drop below their dew point resulting in con-
densation. This condensation (water) then must be drained
from the furnace, and routed to a remote drain, or conden-
sate pump.
The combustion blower creates a negative pressure in ex-
cess of 2²W.C. while operating. Without a condensate drain
trap of sufficient depth, condensate would be held in the fur-
nace, (because of this negative pressure), and not be able
to drain. Figure 26 shows the transition assembly, which is
mounted between the combustion blower and the front parti-
tion.
The condensate drain trap supplied with the furnace MUST
be used. The drain line between the condensate drain trap
and the drain location must be constructed of 3/4²PVC or
CPVC pipe.
In standard Upflow, Counterflow and/or horizontal
installations, the external drain trap provides sufficient
depth (4²) to insure proper drainage of condensate from the
furnace. Additional traps are NOT required, and should NOT
be used. The use of additional traps will PREVENT proper
drainage of condensate from the furnace. Care should be
taken with the routing of the condensate drain hose, to elimi-
nate all dips or sagging tubing which can create another trap,
and cause drainage problems.

Single Stage Multi Position Furnace
Service Manual
18
440 08 2001 02
Figure 26 (Transition Assembly)
25--23--62
NOTE: The vent fitting MUST be installed with the airflow marking
arrow pointed toward the vent pipe, with the drain stub at a 20°
downward slope.(See Figure 27)
Floats and/or condensate sensors are NOT used in the drain
trap. If the drain line becomes clogged, the condensate level
will rise higher in the external trap. When the level rises suffi-
ciently, the furnace will begin to “Cycle” (On and Off) on the
pressure switch. If the condensate level rises high enough
in the trap, the pressure switch may not close at all, and wa-
ter may be heard “Paddling” inside the combustion blower.
Vent Drain
Connection
Figure 27 Condensate Drain Trap
Drain Line
(hidden)
Transition
Box Drain
25--23--63
Vent Drain
Vent Pipe
(Side panel exit)
NEW
OLD
21. HONEYWELL ST9160B Series FAN TIMER/FURNACE CONTROL
Figure 28 Honeywell ST9160B
Dip
Switch
25--23--63
FUSE
The Honeywell ST9160B Electronic Fan Timer/Furnace
Control contains NO USER SERVICEABLE COM-
PONENTS. It is, as its name implies, a fan timer and a fur-
nace control of sorts. In addition to controlling the fan opera-
tion for heating, it also takes the place of the blower relay, the
combustion air relay and/or the system relay.
The ST9160B is used in models equipped with the SV9541M
GAS VALVE/IGNITION CONTROL. It provides the power
source to begin the ignition sequence through a monitored
safety circuit. It also serves as a low voltage terminal strip.
Accessory terminals for connecting a Humidifier and/or
Electronic Air cleaner are also provided, as well as a Contin-
uous fan terminal which allows for continuous fan operation
at a speed other than either the heating or cooling speed.
The control provides a fixed (non--adjustable) 60 second
“ON” and 60 second “OFF” delay for the circulating blower
in COOLING and a 30 second “ON” delay for the circulating
blower in HEATING.
The ST9160B control also provides an adjustable HEATING
“OFF” delay for the circulating blower which can be field ad-
justed to 60, 100, 140, or 180 seconds.