SERVICING
35
S-1 CHECKING VOLTAGE
WARNING
H
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AGE
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ANGING AN
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RICAL WIRING
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IPLE P
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DAMAGE
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NAL INJ
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R DEA
TH.
1. Remove the burner door on furnaces to gain entry to the
Junction Box.
2. Remove cover from the Junction Box and gain access to
incoming power lines.
With Power ON:
L
INE V
O
L
T
AGE N
O
W PRESEN
T
WARNING
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 pow-
er, or faulty Door Interlock Switch from unit to fused
disconnect service. Repair as needed.
5. With ample voltage at line voltage connectors, energize
the furnace blower motor by jumpering terminals R to
G on the integrated ignition control.
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 the service panel doors.
9. Turn on electrical power and verify proper unit opera-
tion.
S-2 CHECKING WIRING
D
ISC
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ALL
P
O
WER
B
E
FO
RE SERVICING
.
WARNING
1. Check wiring visually for signs of overheating, damaged
insulation and loose 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.
2/64 thick insulation of the same gauge or its equivalent.
CHECKING THERMOSTAT, WIRING
AND ANTICIPATOR
S-3A THERMOSTAT AND WIRING
D
ISC
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NNEC
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ALL
P
O
WER
B
E
FO
RE SERVICING
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WARNING
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 (or W1 and W2 for two-stage
models) on the integrated ignition control.
With Power On (and Door Interlock Switch closed):
L
INE V
O
L
T
AGE N
O
W PRESEN
T
WARNING
4. Induced Draft Motor must run and pull in pressure
switch.
5. If the hot surface ignitor heats and at the end of the
ignitor warm-up period 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 blow-
er compartment door.
11. Turn on electrical power and verify proper unit opera-
tion.
S-3B HEATING ANTICIPATOR
On older thermostats 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. Modern
thermostats do not have this type of heat anticipator. Many
have a selector switch to adjust the number of cycles per hour.
