59
SERVICING
CHECKING THERMOSTAT, WIRING AND ANTICIPATOR
S-3A
THERMOSTAT AND WIRING
D
ISCONNECT
ALL
POWER BEFORE SERVICING.
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 VOLTAGE NOW PRESENT
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 ig-
nitor warm-up period the gas valve opens and the
burners ignite, the trouble is in the thermostat or wir-
ing.
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
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 wir-
ing. Repair or replace as necessary.
10. After completing check and/or repair of wiring and
check and/or replacement of thermostat, reinstall
blower compartment door.
11. Turn on electrical power and verify proper unit opera-
tion.
S-3B
HEATING ANTICIPATOR
The heating anticipator on older thermostats 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.
S-4 CHECKING TRANSFORMER AND CONTROL
CIRCUIT
A step-down transformer 120 volt primary to 24 volt second-
ary, 40 VA (Heating and Cooling Models) supplies ample
capacity of power for either operation.
WARNING
HIGH
VOLTAGE
D
ISCONNECT
ALL
POWER BEFORE SERVICING OR
CHANGING ANY ELECTRICAL WIRING.
M
ULTIPLE POWER
SOURCES MAY BE PRESENT.
F
AILURE TO DO SO MAY CAUSE
PROPERTY DAMAGE, PERSONAL INJURY OR DEATH.
1. Remove blower compartment door to gain access to the
thermostat low voltage wires located at the furnace inte-
grated control module.
2. Remove the thermostat low voltage wires at the furnace
integrated control module terminals.
With Power On (and Door Interlock Switch closed):
L
INE VOLTAGE NOW PRESENT
WARNING
3.
Use a voltmeter, check voltage across terminals R
and C. Must read 24 VAC.
4.
No voltage indicates faulty transformer, open fuse, bad
wiring, bad splice, or open door interlock switch.
5.
Check transformer primary voltage at incoming line
voltage connections, fuse, splices, and blower door in-
terlock switch.
6.
If line voltage is available to the primary side of trans-
former and not at secondary side, the transformer is
inoperative. Replace.
7.
After completing check and/or replacement of trans-
former and check and/or repair of control circuit, rein-
stall blower compartment door.
8.
Turn on electrical power and verify proper unit opera-
tion.
L
INE VOLTAGE NOW PRESENT
WARNING
WARNING
HIGH
VOLTAGE
D
ISCONNECT
ALL
POWER BEFORE SERVICING OR
INSTALLING THIS UNIT.
M
ULTIPLE POWER SOURCES MAY
BE PRESENT.
F
AILURE TO DO SO MAY CAUSE PROPERTY
DAMAGE, PERSONAL INJURY OR DEATH.
