SERVICING
59
Rev. 0
S-1 CHECKING VOLTAGE
Disconnect Electrical Power Supply:
1. Remove blower compartment door from furnace to gain
entry to Junction Box.
2. Remove cover from Junction Box to gain access to in-
coming power lines.
With Power ON:
WARNING
LINE VOLTAGE NOW PRESENT.
3. Using a voltmeter, measure the voltage across the hot
and neutral connections.
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, ener-
gize the furnace circulator blower motor.
Note: To energize the furnace, the Door Interlock Switch
must be engaged at this point.
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 opera-
tion.
S-2 CHECKING WIRING
WARNING
Disconnect Electrical Power Supply:
1. Check wiring visually for signs of overheating, dam-
aged insulations and loose or corroded connections.
2. Use 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
ANTICIPATOR
S-3A Thermostat and Wiring
WARNING
Disconnect Electrical Power Supply:
1. Remove 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 fur-
nace integrated control module terminals.
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.
3. Induced Draft Motor must run and pull in pressure
switch.
4. If the hot surface ignitor heats and approximately 17
seconds (White-Rodgers Integrated Control) or 7 sec-
onds (Heatcraft Integrated Control) later the gas valve
opens and the burners ignite, the trouble is in the ther-
mostat or wiring.
5. With power off, check the continuity of the thermostat
and wiring. Repair or replace as necessary.
If the furnace is an air conditioning model and wired for
same, proceed as follows.
6. With power off, Jumper terminals R to Y.
7. Turn on the power
8. 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.
9. After completing check and/or repair of wiring and check
and/or replacement of thermostat, reinstall blower com-
partment door.
10. Turn on electrical power and verify proper unit opera-
tion.
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 the furnaces covered in
this manual are listed in the following chart.
