72
Rev. 2
SERVICING
S-1 CHECKING VOLTAGE
WARNING
Disconnect Electrical Power Supply:
1. Remove blower compartment door from furnace to gain
entry to Junction Box.
2. Remove cover from Junction Box and gain access to
incoming power lines.
With Power ON:
WARNING
LINE VOLTAGE NOW PRESENT.
3. Using a voltmeter, measure the voltage across the hot
and neutral connections.
Note: To energize the furnace, the Door Interlock Switch
must be engaged at this point.
4. No reading - indicates open wiring, open fuse, no power,
or etc. from unit to fused disconnect service. Repair as
needed.
5. With ample voltage at line voltage connectors, energize
the furnace blower motor.
6. With the blower motor in operation, the voltage should
be 115 volts ± 10 percent.
7. If the reading falls below the minimum voltage, check
the line wire size. Long runs of undersized wire can cause
low voltage. If wire size is adequate, notify the local power
company of the condition.
8. After completing check and/or repair, replace Junction
Box cover and reinstall blower compartment door.
9. Turn on electrical power and verify proper unit operation.
S-2 CHECKING WIRING
WARNING
Disconnect Electrical Power Supply:
1. Check wiring visually for signs of overheating, damaged
insulations and loose connections.
2. Using an ohmmeter to check continuity of any suspected
open wires.
3. If any wires must be replaced, replace with AWM, 105°C.
4/64 thick insulation of the same gauge or its equivalent.
S-3 CHECKING THERMOSTAT, WIRING, AND AN-
TICIPATOR
S-3A Thermostat and Wiring
WARNING
Disconnect Electrical Power Supply:
1. Remove the blower compartment door to gain access to
the thermostat low voltage wires located at the furnace
integrated control module terminals.
2. Remove the thermostat low voltage wires at the furnace
control panel terminal board.
3. Jumper terminals R to W on the integrated control mod-
ule.
With Power On (and Door Interlock Switch closed):
WARNING
LINE VOLTAGE NOW PRESENT.
4. Induced Draft Motor must run and pull in pressure switch.
5. If the hot surface ignitor heats and approximately 20 sec-
onds later the gas valve opens and the burners ignite,
the trouble is in the thermostat or wiring.
6. With power off, check the continuity of the thermostat
and wiring. Repair or replace as necessary.
If checking the furnace in the air conditioning mode, pro-
ceed as follows.
7. With power off, Jumper terminals R to Y to G.
8. Turn on the power.
9. If the furnace blower motor starts and the condensing
unit runs, then the trouble is in the thermostat or wiring.
Repair or replace as necessary.
10. After completing check and/or repair of wiring and check
and/or replacement of thermostat, reinstall blower com-
partment door.
11. Turn on electrical power and verify proper unit operation.
S-3B Heating Anticipator
The heating anticipator is a wire wound adjustable heater
which is energized during the "ON" cycle to help prevent
overheating of the conditioned space.
The anticipator is a part of the thermostat and if it should fail
for any reason, the thermostat must be replaced.
The heating anticipator setting for furnaces covered in this
manual are listed in the following chart.
0.70 amps
0.70 amps
GUI_
GCI_
HEATING ANTICIPATOR
