ICP 9MPT, 9MPV, A2î, ìA1, 9MPV050F12A Service Manual

MULTI POSITION

2-- STAGE

GAS FURNACES

This manual supports condensing gas furnaces manufactured in 2001

Manufactured by:

ã 2001 International Comfort Products Corporation (USA)

*9MPT & *9MPV

“A1 & A2”

Part Number

440 08 2002 02

4/2002

*9MPT -- Dual Certified Venting (1 or 2 pipes)

*9MPV -- Dual Certified Venting (1 or 2 pipes)

Variable Speed

ã 2001 International Comfort Products Corporation (USA)

1136 Heil--Quaker Boulevard, LaVergne, TN 37086
All rights reserved throughout the W orld.

Two- Stage Multi Position Furnace

Service Manual

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. L.P. PRESSURE SWITCH 7...................................................

8. HIGH ALTITUDE OPERATION 7...............................................

9. BURNERS 7................................................................

10. CHECKING TEMPERATURE RISE 8..........................................

11. ROOM THERMOSTATS 9....................................................

12. CONTROL WIRING 10.......................................................

13. LIMIT SWITCHES 10.........................................................

14. PRESSURE SWITCHES 12...................................................

15. VENT/COMBUSTION AIR PIPING 13..........................................

16. STANDARD VENT TERMINATION 14..........................................

17. CONCENTRIC VENT TERMINATION 16........................................

18. EXHAUST BLOWER 17......................................................

19. CONDENSATE DRAIN TRAP 17...............................................

20. HONEYWELL ST9162A FAN TIMER/FURNACE CONTROL 18....................

21. ST9162A/SV9541Q TESTING SEQUENCE 19..................................

22. HONEYWELL SV9541Q 2--STAGE GAS VALVE/IGNITION SYSTEM 19............

23. HONEYWELL SV9541Q SYSTEM OPERATION 20..............................

24. CHECKING FLAME CURRENT 22.............................................

25. CAPACITORS 22............................................................

26. BLOWER ASSEMBLY 22.....................................................

27. BLOWER ROTATION 27......................................................

28. HEAT EXCHANGER REMOVAL/REPLACEMENT 38.............................

SV9541Q “SMART VALVE” -- Sequence of Operation 39.............................

SV9541Q “SMART VALVE” -- Trouble shooting 40...................................

SV9541Q “SMART VALVE” -- Electrical Variation 42.................................

TECHNICAL SERVICE DATA (N9MPV) 44.........................................

BLOWER PERFORMANCE DATA (*9MPV) 45......................................

TECHNICAL SERVICE DATA (*9MPT) 52..........................................

BLOWER PERFORMANCE DATA (*9MPT) 53......................................

WIRING DIAGRAM (*9MPV) 54...................................................

WIRING DIAGRAM (*9MPT) 58...................................................

APPENDIX OF HELPFUL INFORMATION 60.......................................

Service

Manual

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 elec­tronic components which are not user serviceable. there-
fore, 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 any malfunction of this product.

This service manual covers several different models in two
(2) families of our new multi--position furnaces; Variable
Speed (D.C.-- Blower Motor) models in the Condensing fur­nace family, and 2 speed (P.S.C.--Blower Motor) models in
both the Condensing and Non--Condensing furnace families.
The overall operation of all of these models and families is
essentially the same, with the exception of the Blower Motor,
and/or certain control functions which may be unique to a
particular model and/or family.

Two- Stage Multi Position Furnace

ELS”. G ENE RALLY, t he dist inct ion between t hese two
groups is based on a difference in the type of Blower Motor
used. These may not be the only differences, however,
and the differences may vary from model to model within a
particular family or series.

It will be necessary then for you to accurately identify the
unit you are servicing, so you may be certain of a proper
diagnosis and repair. (See Unit Identification, Page 3)

!

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 repairsto 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.

This manual, therefore, will deal with all subjects in a general
nature (I.E. all text will pertain to all models) unless that sub­ject is unique to a particular model or family, in which case
it will be so indicated.

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

Throughout the manual references may be made to “VARI-

and/or service procedures.

ABLE SPEED MODELS” as well as “TWO SPEED MOD-

2. UNIT IDENTIFICATION

The unit’s rating plate contains important information for the
service technician. It also lists the complete Model Manufac­turing and Serial Numbers.

These complete numbers are required to obtain correct re-

MODEL NUMBER IDENTIFICATION GUIDE

* 9 MP T 075 B 12 A 1

Brand Identifier Engineering Rev.

T=Tempstar N=Neture Denotes minor changes

C = Comfortmaker/Keeprite Marketing Digit

H = Heil/Arcoaire X = Evaluation Denotes minor change

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 Cabinet Width

MP = Multiposition, Upflow/Downflow/Horizontal B = 15.5² Wide

Major Design Feature F = 19.1² Wide

1 = One (Single) Pipe L= Low NOx T = Two Stage J = 22.8² Wide

2 = Two Pipe N = Single Stage V = Variable Speed L = 24.5² Wide

D = 1 or 2 Pipe P = PVC Vent Input (Nominal MBTUH)

440 08 2002 02

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.

Cooling Airflow

2

Two- Stage Multi Position Furnace

Service

Manual

Figure 1

Furnace Vent Pipe
(Vent Pipe Connection through
Side Panel on Some Models)

Vent Pipe Grommet

Manual Gas Valve

Rating Plate

Vent Drain Fitting

Diagnostic Light

Combustion Air Blower

Condensate Trap

3

/4²²²² OD Transition Box

Drain Hose

Component Locations for Four Position Furnaces

5

/8²²²² OD Vent Pipe

Drain Hose

Door Interlock Switch

Air Intake Pipe
(Dual Certified or Direct
Vent furnaces)

Primary Heat Exchanger

Secondary Heat Exchanger

Gas Valve/Ignition Module

Pressure Switches

Plastic Transition Box

Coils Air Baffle

Circulating Air Blower

Fan/Delay Control

3. FURNACE THEORY OF OPERATION

The high efficiencies and lower profile (compared to previous
series) of this furnace have been obtained using design tech­niques not typical of traditional furnace designs. A brief de­scription 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 work­ing the heat exchanger more efficiencly and yet mini­mizing the overall size.

The design required to achieve these results is the “SER­PENTINE” 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 follow­ing reasons:

A.The s econdary combustion airflows at right angles to the

burner flame, making it likely to “pull” the flame off a ribbon
or slotted port type burner.

D C Motor Control
(some models)

dwg 25-- 23--29a

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 exchanger 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 pos­sible from the flue gasses, a secondary heat exchang­er (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, thus increasing operating effi­ciency of the furnace, and the term “Condensing Fur-
nace”. 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.

440 08 2002 02

3

Service

Manual

Two- Stage Multi Position Furnace

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.

4. ELECTRICAL SUPPLY

!

Electrical shock hazard.

Turn OFF electric power at fuse box or service panel
before making any electrical connections and en­sure 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.

7. 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.

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 con­nection 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.

Figure 2

Electrical Connections

W2

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.

POLARITY

CORRECT POLARITY of the line voltage supply to all fur­naces is also 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.

W2

W2

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.

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 poten­tial 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) Vo ltage.(ifzero
volts is read, there is no ground, or polarity is re­versed.)

440 08 2002 02

4

Two- Stage Multi Position Furnace

T

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 op­eration when the door is open. This interlock switch is a safe­ty 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)

6. GAS SUPPLY

Figure 3

Service

Typical Interlock Switch

Manual

10--12--96

On/Off
Switch

Manifold Pressure
Adjustment

OUTLET

INLET

Typical Gas Valve HoneywellFigure 4

Manifold
Adjustment
(Hidden)

LO

HI

INLET

25--22--49a

Diagnostic Light
(on some models)

Pilot
Adjustment

OUTLET

25--22--25a

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 4.5² W.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 11² W.C. If this
cannot be obtained, problems are indicated in either the reg­ulator or pipe sizing.

Tab l e 1 Gas Pressures Below 2000¢¢¢¢

Gas

ype

Recommended Max. Min. Hi Fire Lo Fire

Natural 7² 14² 4.5² 3.5² 1.7²

LP 11² 14² 11² 10² 4.9²

· With Propane gas, the rated input is obtained when the
BTU content is 2,500 BTU per cubic foot and manifold
pressure set at 10²²²² W.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.

Supply Pressure

Important Note:

Manifold

Pressure

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 standards.

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 ad­justing (as necessary) the manifold (Outlet) pressure. The
second way is to “Clock” the gas meter.

440 08 2002 02

5

Service

Btu/C

u.F

t

Manual

Two- Stage Multi Position Furnace

!

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.

Gas Pressure Testing DevicesFigure 5

Pressure Connections

3

2

1

0

1

2

3

0

INCHES OF WATER

510

15

MAGNEHELIC

MAX. PRESSURE 15 PSIG

CHECKING MANIFOLD PRESSURE

1. Connect manometer or Magnehelic gauge to the
tapped opening on the outlet side of gas valve. Use a
manometer witha0to12² minimum water column
range.

2. Turn gas ON. Operate the furnace on high fire by using
a jumper wire on the R to W1 & W2 thermostat connec­tions on the fan board.

3. Remove the adjustment cover on the gas valve. Turn
adjusting screw counterclockwise to decrease the
manifold pressure and clockwise to increase. See
Figure 4.

4. Set the manifold pressure to value shown in Table 1 or
Tab l e 2.

5. Operate the furnace on low fire by using a jumper wire
on the R to W1 thermostat connections on the fan
board.
Note: The fourth (4th) DIP switch should be in the on
position to set the low fire manifold pressure. (See wir­ing digram)

6. Repeat steps 4 and 5 for low fire operation.

7. When the manifold pressures are properly set, replace
the adjustment screw covers on the gas valve.

8. Remove the jumper wires from the thermostat connec-

Typical "U" Tube

Manometer

tions on the fan board. Remove manometer and re­place plug in gas valve.

9. Reture fourth (4th) DIP switch to previous setting.

10. Replace the burner compartment door.

MANIFOLD PRESSURE AND ORIFICE SIZE FOR HIGH ALTITUDE APPLICATIONS

Tab l e 2

HeatValue

.

800 3.5 1.7 3.5 1.7 3.5 1.7 3.5 1.7 3.5 1.7 3.5 1.7 3.5 1.7

850 3.5 1.7 3.5 1.7 3.5 1.7 3.5 1.7 3.5 1.7 3.5 1.7 3.5 1.7

900 3.5 1.7 3.5 1.7 3.5 1.7 3.5 1.7 3.5 1.7 3.5 1.7 3.4 1.7

950 3.5 1.7 3.5 1.7 3.5 1.7 3.5 1.7 3.3 1.6 3.2 1.6 3.1 1.5

1000 3.5 1.7 3.4 1.7 3.3 1.6 3.2 1.5 3.0 1.5 2.9 1.4 2.8 1.4

1050 3.2 1.6 3.1 1.5 3.0 1.5 2.9 1.4 2.7 1.3 2.6 1.3 2.5 1.2

1100 2.9 1.4 2.8 1.4 2.7 1.3 2.6 1.3 2.5 1.2 2.4 1.2 2.3 1.1

Orifice Size #42 #42 #42 #42 #42 #42 #42

0-- 1999 2000-- 2999 3000--3999 4000-- 4999 5000-- 5999 6000-- 6999 7000-- 7999

High Low High Low High Low High Low High Low High Low High Low

“CLOCKING” GAS METER (NATURAL GAS)

1. Check with gas supplier to obtain ACTUAL BTU con­tent of gas.

2. Turn “OFF” gas supply to ALL other gas appliances.

High Altitude Pressure Chart

2000--8000 ft. (Natural Gas)

Elevation Above Sea Level

5. Operate furnace on LOW fire, and time how many se­conds it takes the smallest (normally 1 cfh) dial on the
gas meter to make one complete revolution.

6. Calculate LOW fire input rate by using ACTUAL BTU
content of gas in formula shown in example.

3. Operate furnace on HIGH fire, and time how many se­conds it takes the smallest (normally 1 cfh) dial on the
gas meter to make one complete revolution.

4. Calculate HIGH fire input rate by using ACTUAL BTU
content of gas in formula shown in example.

440 08 2002 02

6

Example

Natural Gas

BTU Content

1,000 3,600 48 75,000

No. of Seconds

Per Hour

1,000 x 3,600 ¸ 48 = 75,000 BTUH

Time Per Cubic

Foot in Seconds

BTU Per

Hour

Two- Stage Multi Position Furnace

7. L.P. PRESSURE SWITCH

Models converted to operate on L.P. Gas will be installed
with an L.P. Pressure Switch. 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 un­der low line (Supply) pressure conditions. Operating under
low line pressure conditions, can create problems such as in­complete combustion, flashback, sooting, etc.

The switch is a “Normally Open” pressure operated switch
that is wired in series with the furnace (Lo--fire) pressure
switch. The L.P. Pressure Switch closes when line (Supply)
pressure is 8.0² W.C. or higher. the L.P. Pressure Switch

Opens if line pressure falls below 6.0²+0.6² W.C. interrupt­ing power to the gas valve.

It is located (electrically) between the Main Limit Switch and
the furnace (vent) pressure switch. The switcht is located
(electrically) between the Furnace (Lo--fire) pressure switch
and the gas Valve.

8. 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 in­sure continued, safe reliable operation. For example, units
must be de--rated for altitude (by adjusting manifold pres­sure 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.

Service

Figure 6

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¢ in­sure that it has been properly modified to operate at that alti­tude. See the sections on Gas pressure, and pressure
switches to obtain specific information for you particular
installation altitude.

Typical L.P . Pressure Switch

Manual

9. 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 burner box design. In order to insure that the burners
are operating properly , and at their design noise level, proper
adjustment of the gas (manifold) pressure is essential. For
further information on manifold pressure adjustments check
the section on “Gas Supply”.

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.

Figure 7

Main Burner

Burner Face

10-- 10--78

440 08 2002 02

7

Service

50Mbt

75Mbtu,100Mb

tu&125Mbt

50Mbt

75Mbtu,100Mb

tu&125Mbt

Manual

10. CHECKING TEMPERATURE RISE

Two- Stage Multi Position Furnace

Figure 8

Thermometer:
Return Air Temp.

Return

Air Flow

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 prema­ture 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.

Checking Temperature Rise

Supply

Air Flow

Thermometer;
Supply Air Temp.

2- STAGE MODELS

Model Fire Range

u

Always check current “Technical Support Manual”

HI 35°F--65°F

LOW 25°F--55°F

HI 40°F--70°F

u

LOW 30°F--60°F

ALLOWABLE TEMPERATURE RISE FOR
VARIABLE SPEED MODELS

Model Fire Range

u

Always check current “Technical Support Manual”

Operate the furnace for 15 minutes before taking tempera­ture 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 ther­mometer in the supply duct at lease two (2) ft. away from the
furnace. (This will prevent any false readings caused by radi­ation 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 T emp. 170
Return Temp. 70°
Temperature Rise 100° = Too High

HI 35°F--65°F

LOW 35°F--65°F

HI 40°F--70°F

u

LOW 40°F--70°F

°

ALLOWABLE TEMPERATURE RISE FOR

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 de­sired conditions.

440 08 2002 02

Solution: Increase Blower Speed

An improperly operating, or poorly located room thermostat
can be the source of perceived equipment problems. A care­ful check of the thermostat and wiring must be made then to
insure that it is not the source of problems.

8

Two- Stage Multi Position Furnace

Service

Manual

Figure 9

Thermostat Location

DRAFTS

THERMOSTAT

SUN

SHIELD

5 ft.

LIGHT

LOCATION

The thermostat should not be mounted where it may be af­fected by drafts, discharge air from registers (hot or cold), or
heat radiated from the sun of appliances. Never install in al­coves, 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 tem­perature accurately to the desired set--point. Electronic digi­tal 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 pre­vent wide swings in room temperature during furnace opera­tion.

In order to accomplish this, the heat output from the anticipa­tor must be the same regardless of the current flowing
through it. Consequently , most thermostats have an adjust­ment to compensate for varying current draw in the thermo­stat circuit.

The proper setting of heat anticipators then is important to
insure proper temperature control and customer satisfac­tion.

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.

Figure 10

Measuring Current Draw

W

Amps

R

Subbase

Ammeter

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” termi­nal.

3. Turn power on, and wait approximately 1 minute, then
read meter.

4. Divide meter reading by 10 to obtain correct anticipator
setting.

NOTE: For 2 Stage heating thermostats the above proce-

dure MUST be perform ed twic e. Once for first
stage (W

1), and once f or s econd st age (W2), if

both stages have adjustable heat anticipators.

If an ammeter is not available, a setting of 0.10 amps may
be used for models equipped with the HONEYWELL
SV9541Q Gas Valve/Ignition Control. They should, howev­er, provide satisfactory operation in most cases.

Electronic thermostats do not use a resistance type anticipa­tor. 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.

440 08 2002 02

9

Service

Manual

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. It is often
overlooked as the source of equipment malfunctions. Con­trol wiring that is either too long, undersized, or improperly
connected (be it simply loos e, or on the wrong terminal)
can in fact be the source of many equipment problems.

Two- Stage Multi Position Furnace

operation, the furnace will shift from low fire to high fire as
requested by the thermostat. The thermostat heat anticipa­tors should be adjusted to a .10 setting for both types of ther­mostats.

Low voltage connections to furnace must be made on termi­nal board to fan control.

ALWA YS check to make sure that the control wiring is con­nected to the proper terminal(s) of the equipment and ther­mostat you are using. Remem ber, also, that therm ost at
terminals are not always identified alike by different ther­mostat manufacturers. Connections MUST be clean and
tight to insure trouble--free operation.

The controls of this series of 2--Stage furnaces ar e de­signed to provide 2--Stage operation using a Two (2) Stage
Thermostat, ONLY as follows:

The 2--stage furnace control will operate with either a single
stage or a two stage heating thermostat and will provide
2--stage heating operation. For single stage thermostat
installations, the R and W wires from the thermostat connect
to the R and W1 connections on the furnace control. Note:
The fourth (4th) DIP switch must be in the off position, failure
to change DIP switch will result in Lo Fire ONLY operation.
(See furnace wiring digram) See “Furnace Wiring Diagram”
for switch settings. Failure to set DIP switch will result in Lo
fire operation ONLY with single stage thermostat. During op­eration, the furnace will operate on low fire for 12 minutesIf
the heat request exists for more than 12 minutes. If the heat
request exists for more that 12 minutes, the furnace will auto­matically shift to the high fire mode for the remaining duration
of the heating cycle. For two stage thermostat installations,
the R, W1 and W2 wires from the thermostat connect to the
R, W1 and W2 connections on the furnace control. During

The ELECTRO NI C CONTROLS used on t his series RE­SPOND DIFFERENTL Y to certain control wiring practices
which have been generally accepted in the HVAC industry
for many years.

For Example: For years, installers have run a wire from the
“Y” t er m inal of the room thermost at and connec t ed it di­rectly to the contactor coil of a condensing unit. (not mak­ing any connection to the furnace with this wire) Then, run
the low voltage “Common” wire from the condensing unit
back to the “C” terminal of the furnace.

With the HONEYWELL ST9162A electronic Fan Timer/
Furnace Control used in the models of this series, howev­er, 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:

The COOLING fan speed is energized via the “Y” terminal.
Failure to connect the thermostat “Y” terminal to the “Y”
terminal on the control will result in the failure to energize
the COOLING speed on a call for cooling from the thermo­stat. (Depending upon the model, either the LOW HEAT­ING speed or the CIRCULATING speed will be energized
instead via the “G” terminal)

For more detailed information about this control, see the
section on the ST9162A control beginning on page 23 of
this manual.

13. LIMIT SWITCHES

Two (2) different kinds of limit switches are used on this se­ries of furnaces. They are the main limit and roll out limit
switches. The main limit, and roll out 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, de­signed 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-

440 08 2002 02

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:

10

Two- Stage Multi Position Furnace

Service

Manual

MAIN LIMIT SWITCH

A “Normally Closed” switch located on the front partition of
the furnace. It monitors supply air temperature, and inter­rupts furnace (burner) operation when a supply air tempera­ture 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 blow­er will be energized continuously. This control is an “Auto­matic” reset control, which will reset itself when the tempera­ture 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.)

Figure 11

Typical Limit Switch

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 set­ting. 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 LIMITS

Those “Normally Closed” unit switches (wired in series with
the Main Limit switch) on the top are mounted on the bottom
(left & right) of the burner box.

The switches are manual reset type. When replacing this
switch, be absolutely certain the correct one is used.

Figure 12

Typical Roll Out Limit Switch

To verify this, the cut--out (opening) point of the switch should
be checked (using a thermocouple type thermometer con­nected 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 sim­ply doing its job, and the cause of the over--temperature must
be determined and corrected.

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 intermit­tent operation.

The roll out switch monitors the temperature inside the burn­er 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 deter­mined. Some possible reasons for flame roll out include a re­stricted primary or secondary heat exchanger or over fired
furnace.

MANUAL RESET SWITCH MODELS

Furnace models which are equipped with a Honeywell
ST9162A Fan timer/furnace control use a manual reset roll
out switch. Once the roll out switch has opened, burner op­eration will be prevented until the roll out switch is “Manually
Reset” 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.

440 08 2002 02

11

Service

Manual

14. PRESSURE SWITCHES

Two- Stage Multi Position Furnace

TRANSITION PRESSURE SWITCH

Under normal operating conditions, sufficient pressure is de­veloped 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 re­duce. When the pressure drops sufficiently, burner operation
will be prevented until the condition is corrected.

STANDARD PRESSURE SWITCHES - ALL

MODELS

Model

Condensing
50, 75 &100

125

Always check current “Technical Support Manual”for
Part Nos.

Max.

Close

--1.70² W.C.

--2.00² W.C.

Open Part #

--1.50 + 0.10² W. C .

--

--1.80 + 0.10² W.C .

--

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.

Note: Transition switch checks lo--fire airflows & blocked
condensate. Blower switch checks Hi--fire airflow.

HIGH ALTITUDE PRESSURE SWITCHES - ALL

MODELS

Model

Condensing
50, 75 &100

125

Always check current “Technical Support Manual”for
Part Nos.

Under normal operating conditions, sufficient negative pres­sure will be created to close the pressure switch, and keep
it closed to keep furnace operating. Under abnormal condi­tions, 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 fail­ing to remain closed during furnace operation.

440 08 2002 02

Max.

Close

--1.40² W.C.

--1.70² W.C.

Open Part #

--1.20 + 0.10² W.C .

--

--1.50 + 0.10² W.C .

--

1013165

1013157

Figure 13

Pressure Switches

Blower
(Hi--fi re)

Transition
(Lo--fire)

25--23--72

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 Tab l e 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 pressure
should ONLY be checked when “HOT” to insure accurate
readings.

Tab l e 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 pres­sures against. The pressures you obtain in the field will differ
slightly from these figures based upon vent length, gas pres­sure, operating temperature, etc.

Major discrepancies in pressures, will normally cause
problems with pressure switch operation. These Major dis­crepancies should be investigated as follows:

12

Two- Stage Multi Position Furnace

50Mbtu&

100Mb

t

Table 3 APPROXIMATE OPERATING PRESSURES (INCHES OF W.C.)

@Blower/@Transition

Model Vent Length (High Fire) (Low Fire)

50 Mbtu &

75 Mbtu

u

125 Mbtu

Always check current “Technical Support Manual”for
updated information.

Short -- (5 Ft. No Elbows) --1.80/--2.60 --1.20/--1.90
Long -- (40 Ft. + 5 90° Elbows) --1.30/--2.30 --1.00/--1.80
Short -- (5 Ft. No Elbows) --1.80/--2.60 --1.20/--1.90
Long -- (40 Ft. + 5 90° Elbows) --1.70/--2.50 --1.00/--1.80
Short -- (5 Ft. No Elbows) --1.80/--2.60 --1.30/--2.30
Long -- (40 Ft. + 5 90° Elbows) --1.70/2.50 --1.20/--2.20

2. Leak (lack of restriction) on the Inlet side of the com­bustion blower.

Service

Manual

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 blow­er. (I.E. Blocked Flue, Vent too long, Heat Exchanger
leak, etc.)

Figure 14

UPFLOW

*8² Min.
20¢ Max.
in same
atmospheric zone

Vent Pipes MUST be
supported Horizontally
and Vertically

Typical Vent/Combustion Air Piping Installation

Aluminum or non-- rusting shield recommended.
(See Vent Termination Shielding for dimensions).

Inlet Pipe

DISCHARGE AIR

Coupling on ends of exhaust
pipe. Total pipe & coupling
outside structure = 8²

*8² Min.
20¢ Max.
in same atmospheric zone

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)

DOWNFLOW

Inlet Pipe

Vent Pipes MUST
be supported
Horizontally and
Vertically

See Vent Termination Shielding
in Vent Section.

*8² Min.
20¢ Max.
in same
atmospheric
zone

Coupling on inside and
outside of wall to
restrain vent pipe

8² Min.

*8² Min.
20¢ Max.
in same
atmospheric zone

* Increase minimum from 8² to 18² for cold climates (sustained temperatures below 0 ° F).

15. 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

25--23--33

* Increase minimum from 8² to 18² for cold climates (sustained temperatures

below 0°F).

25--23--33a

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 struc­ture.

440 08 2002 02

13

Service

Manual

Two- Stage Multi Position Furnace

DUAL CERTIFIED models require a combustion air inlet
pipe to bring in all air for combustion from outside the struc­ture only when installed as a Direct Vent Furnace (I.E. Two
Pipe Installation)

16. STANDARD VENT TERMINATION
Vent/Combustion Air Piping Charts

Single Piping Chart

Tab l e 4

50,000 & 75,000 Btuh Furnaces

40¢ & (5) 90° elbows with 2² PVC pipe

100,000 & 125,000 Btuh Furnace

40¢ & (5) 90° elbows with 3² PVC pipe

Elbows are DWV Long Radius Type for 2² and 3² vents.

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.

Dual Piping Chart

Tab l e 5

50,000 & 75,000 Btuh Furnaces

40¢ & (5) 90° elbows with 2² PVC pipe

100,000 & 125,000 Btuh Furnace

40¢ & (5) 90° elbows with 3² PVC pipe

Elbows are DWV Long Radius Type for 2² and 3² vents.

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

Pipe Diameter Table
Single Piping ONLY

Pipe Diameter Table

Dual Piping ONLY

Standard Termination

Rooftop Termination

B

Consult the appropriate Venting tables and/or piping chart
for the model (series) you are servicing.

Figure 16

Inlet is optional on
Dual Certified models

Figure 17

12²²²² Min. Grade
or Snow Level

Dimension “A” is touching or 2² maximum separation.

Figure 18

Sidewall Termination 12² or More
Above Snow Level or Grade Level

8² *

MIN.

20’

MAX

*18² Minimum for cold climates

(substained below 0° F)

Concentric Vent and Combustion-­Air Roof Termination

Exhaust

Combustion

Air

“A”

Concentric Vent and Combustion-­Air Sidewall Termination

25-- 00--05F

Inlet is optional on
Dual Certified models

A

A

A=12² Above roof or snow accumulation level
B=8² Min., 20¢ Maximum, except in areas with extreme
cold temperatures (sustained below 0°F), the 18² Min.

440 08 2002 02

25-- 00--06

14

1²²²² Maximum

Combustion Air

Exhaust

Ven t

Dimension “A” is touching or 2² maximum separation.

(TYP.)

Ven t

“A”

25--22--02d

Two- Stage Multi Position Furnace

Service

Manual

Figure 19

“A”

Inlet

12²²²² Min. Grade
or Snow Level

Dimension “A” is touching or 2² maximum separation.

Figure 20

18²²²² Min. for Cold Climates

(Sustained Below 0°°°° F)

Exhaust

Sidewall Inlet Vent and Exhaust-­Air Termination

Exhaust

8²²²² Min.
20¢¢¢¢ Max.

18²²²² Min. for

Cold Climates

(Sustained Below 0°°°° F)

“A”

8²²²² Min.

Sidewall Inlet Vent and Exhaust--Air
Termination with Exterior Risers

8²²²² Min.

8²²²² Min.
20¢¢¢¢ Max.

12²²²² Min.
Grade or

Inlet

Snow Level

Figure 22

FRONT VIEW

Recommended Alternate Installa­tion for Sustained Cold Weather
(--0°°°° F & below)

OVERHANG

12²²²² MIN.

EXHAUST

90°°°°

INLET

12²²²² MIN. Ground Level

OR Snow Level

SIDE VIEW

12²²²² MIN.

25--23 --73

Figure 21

18²²²² Min. for Cold Climates

12²²²² Min.
Grade or
Snow Level

“A”

“A”

Dimension “A” is touching or 2² maximum separation.

Rooftop Inlet Vent and Exhaust-­Air Termination

(Sustained Below 0°°°° F)

Inlet

8²²²² Min.
20¢¢¢¢ Max.

Exhaust

Same Joist

Space

25--22--43

440 08 2002 02

15

Service

Manual

17. CONCENTRIC VENT TERMINATION

Two- Stage Multi Position Furnace

Vent/Combustion Air Piping Charts

Concentric Termination Kit NAHA001CV

Tab l e 6

NAHA002CV -- 35¢ & (4) 90° elbows with 2² PVC pipe

NAHA001CV -- 35¢ & (4) 90° elbows with 3² PVC 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 2

Figure 23

& NAHA002VC Venting Table Dual Piping

ONLY

50,000 & 75,000 Btuh Furnaces

100,000 & 125,000 Btuh Furnace

² and 3² vents.

Concentric Vent Roof Installation

Vent

Combustion
Air

Roof Boot/
Flashing
(Field Supplied)

Maintain 12² min. clearance
above highest anticipated
snow level. Max. of 24²
above roof.

Figure 24

3² x2² Bushings or

1

/2² Bushings

3² x2
If 3² vent not used
(Field supplied)

Vent

Combustion
Air

Note:

Securing strap must be field installed to prevent movement of termina­tion kit in side wall.

Concentric Vent Sidewall
Attachment

Strap
(Field Supplied)

45° Elbow
(Field Supplied)

Combustion
Air

Vent

Flush to
1² max.

25-- 22--02

Support
(Field Supplied)

45° Elbow
(Field Supplied)

Vent

Combustion
Air

Note:

Support must be field installed to secure termination kit to structure.

25-- 22--02

440 08 2002 02

16

Two- Stage Multi Position Furnace

18. EXHAUST BLOWER

Figure 25

Exhaust Blower

Service

Manual

Always check the current “Technical Support Manual” for
part nos.

Vent Fitting
&Clamps

90° Elbow

Vent Pipe
(Side panel exit)

Vent Fitting
&Clamps

DRAIN SIDE VIEW

C

L

Rotate
downward
20° to 30°

Vent Pipe (Top panel exit)

Rubber Coupling & Clamps

Blower

25-- 23--35

19. CONDENSATE DRAIN TRAP

This furnace removes both sensible and latent heat from the
products of combustion. Removal of the latent heat results in
condensation of the water vapor. The condensate is re­moved from the furnace through the drains in the plastic tran­sition and the vent fitting. The drains connect to the external­ly mounted condensate drain trap on the left or right side of
the furnace. Refer to Figure 26.

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
CPVC pipe.

The drain line must maintain a

1

/4² per foot downward slope

toward the drain.

3

/4² PVC or

Figure 26 External Drain Trap

Vent Pipe
(Side panel exit)

Vent Drain Connection

Drain Line
(hidden)

Vent Drain

OLD

Transition
Box Drain

DO NOT trap the drain line in any other location than at the
condensate drain trap supplied with the furnace.

If possible DO NOT route the drain line where it may freeze.
The drain line must terminate at an inside drain to prevent
freezing of the condensate and possible property damage.

1. A condensate sump pump MUST be used if required
by local codes, or if no indoor floor drain is available.
The condensate pump must be approved for use with
acidic condensate.

2. A plugged condensate drain line or a failed condensate
pump will allow condensate to spill. If the furnace is
installed where a condensate spill could cause dam­age, it is recommended that an auxiliary safety switch
be installed to prevent operation of the equipment in
the event of pump failure or plugged drain line. If used,
an auxiliary safety switch should be installed in the R
circuit (low voltage) ONLY.

17

NEW

25--23--63

440 08 2002 02