ICP 9MPT Series User manual

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

*9MPT -- Dual Certified Venting (1 or 2 pipes)
*9MPV -- Dual Certified Venting (1 or 2 pipes)
Variable Speed
ã2001 International Comfort Products Corporation (USA)
1136 Heil--Quaker Boulevard, LaVergne, TN 37086
All rights reserved throughout the World.

Service Manual
Two- 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. 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.......................................

Two- Stage Multi Position Furnace
Service Manual
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440 08 2002 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 several different models in two
(2) families of our new multi--position furnaces; Variable
Speed (D.C.-- Blower Motor) models in the Condensing fur-
nace 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.
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.
Throughout the manual references may be made to “VARI-
ABLE SPEED MODELS” as well as “TWO SPEED MOD-
ELS”. GENERALLY, the distinction between these 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 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 T075 B12 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
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 Cabinet Width
MP = Multiposition, Upflow/Downflow/Horizontal B = 15.5²Wide
Major Design Feature F = 19.1²Wide
1 = One (Single) Pipe L= Low NOx T = Two Stage J = 22.8²Wide
2 = Two Pipe N = Single Stage V = Variable Speed L = 24.5²Wide
D = 1 or 2 Pipe P = PVC Vent Input (Nominal MBTUH)

Two- Stage Multi Position Furnace Service Manual
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440 08 2002 02
Component Locations for Four Position Furnaces
Figure 1
Circulating Air Blower
Rating Plate
Gas Valve/Ignition Module
Door Interlock Switch
Pressure Switches
Fan/Delay Control
Furnace Vent Pipe
(Vent Pipe Connection through
Side Panel on Some Models)
Combustion Air Blower
Vent Pipe Grommet
Primary Heat Exchanger
Secondary Heat Exchanger
dwg 25--23--29a
Diagnostic Light
Manual Gas Valve
Vent Drain Fitting
3/4
²
²²
²OD Transition Box
Drain Hose
5/8
²
²²
²OD Vent Pipe
Drain Hose
Plastic Transition Box
Air Intake Pipe
(Dual Certified or Direct
Vent furnaces)
Condensate Trap
D C Motor Control
(some models)
Coils Air Baffle
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 work-
ing the heat exchanger more efficiencly and yet mini-
mizing 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 im-
pingement 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 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, thus increasing operating effi-
ciency of the furnace, and the term “Condensing Fur-
nace”. This results in the forming of condensation (wa-
ter) 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.

Two- Stage Multi Position Furnace
Service Manual
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440 08 2002 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. 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 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.
POLARITY
CORRECT POLARITY of the line voltage supply to all fur-
naces 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.
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.
Figure 2 Electrical Connections
W2
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 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.)

Two- Stage Multi Position Furnace Service Manual
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440 08 2002 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
INLET
OUTLET
Diagnostic Light
(on some models)
25--22--25a
On/Off
Switch
Pilot
Adjustment
Manifold
Adjustment
(Hidden)
Manifold Pressure
Adjustment
INLET
OUTLET
25--22--49a
LO HI
An adequately sized gas supply to the furnace is required for
proper operation. Gas piping which is undersized will not pro-
vide sufficient capacity for proper operation. Piping should
be sized in accordance with accepted industry standards.
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
y
p
e
Supply Pressure Manifold
Pressure
T
ype Recommended Max. Min. Hi Fire Lo Fire
Natural 7²14²4.5²3.5²1.7²
LP 11²14²11²10²4.9²
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.

Two- Stage Multi Position Furnace
Service Manual
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440 08 2002 02
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
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 manometer or Magnehelic gauge to the
tapped opening on the outlet side of gas valve. Use a
manometer witha0to12²minimum 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 connec-
tions 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
Table 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 wir-
ing 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-
tions on the fan board. Remove manometer and re-
place 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
Table 2 High Altitude Pressure Chart
2000--8000 ft. (Natural Gas)
H
t
V
l
Elevation Above Sea Level
Heat
V
alue
B
t
u
/
C
u
.
F
t
.
0--1999 2000--2999 3000--3999 4000--4999 5000--5999 6000--6999 7000--7999
B
t
u
/
C
u
.
F
t
.
High Low High Low High Low High Low High Low High Low High Low
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
“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. Operate furnace on HIGH fire, and time how many se-
conds 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.
5. Operate furnace on LOW fire, and time how many se-
conds 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.
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

Two- Stage Multi Position Furnace Service Manual
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440 08 2002 02
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 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 (Lo--fire) pressure
switch. The L.P. Pressure Switch closes when line (Supply)
pressure is 8.0²W.C. or higher. the L.P. Pressure Switch
Opens if line pressure falls below 6.0²+0.6²W.C. interrupt-
ing 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.
Typical L.P. Pressure Switch
Figure 6
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 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, and pressure
switches to obtain specific information for you particular
installation altitude.
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.
Main Burner
Burner Face
10--10--78
Figure 7

Two- Stage Multi Position Furnace
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440 08 2002 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 FOR
2- STAGE MODELS
Model Fire Range
5
0
M
b
t
u
HI 35°F--65°F
5
0
M
b
t
uLOW 25°F--55°F
7
5
M
b
t
u
1
0
0
M
b
t
u
&
1
2
5
M
b
t
u
HI 40°F--70°F
7
5
M
b
t
u,
1
0
0
M
b
t
u
&
1
2
5
M
b
t
uLOW 30°F--60°F
Always check current “Technical Support Manual”
ALLOWABLE TEMPERATURE RISE FOR
VARIABLE SPEED MODELS
Model Fire Range
5
0
M
b
t
u
HI 35°F--65°F
5
0
M
b
t
uLOW 35°F--65°F
7
5
M
b
t
u
1
0
0
M
b
t
u
&
1
2
5
M
b
t
u
HI 40°F--70°F
7
5
M
b
t
u,
1
0
0
M
b
t
u
&
1
2
5
M
b
t
uLOW 40°F--70°F
Always check current “Technical Support Manual”
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.