48
SERVICING
Cooling Anticipator
The cooling anticipator is a small heater (resistor) in the
thermostat. During the "OFF" cycle it heats the bimetal
element helping the thermostat call for the next cooling cycle.
This prevents the room temperature from rising too high
before the system is restarted. A properly sized anticipa-
tor should maintain room temperature within 1 1/2 to 2
degrees.
The anticipator is fixed in the subbase and is not to be
replaced. If the anticipator should fail for any reason, the
subbase must be changed.
S-4 CHECKING TRANSFORMER AND Control CIR-
CUIT
A step-down transformer 120 volt primary to 24 volt sec-
ondary, 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
integrated 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
interlock switch.
6.
If line voltage is available to the primary side of
transformer and not at secondary side, the trans-
former is inoperative. Replace.
7.
After completing check and/or replacement of trans-
former and check and/or repair of control circuit, re-
install blower compartment door.
8.
Turn on electrical power and verify proper unit op-
eration.
S-10
Capacitance Check
With power On (and Door Interlock Switch closed):
L
INE VOLTAGE NOW PRESENT
WARNING
S-15
CHECKING CAPACITOR
The direct drive motors are of the permanent split capacitor
design. A run capacitor is wired across the auxiliary and a
portion of the main windings. The capacitors primary func-
tion is to reduce the line current while greatly improving the
torque characteristics of a motor. This is accomplished by
using the 90° phase relationship between the capacitor cur-
rent and voltage in conjunction with the motor windings so
that the motor will give two phase operation when connected
to a single phase circuit. The capacitor also reduces the
line current to the motor by improving the power factor to
the load.
WARNING
D
ISCHARGE CAPACITOR THROUGH A 20 TO 30 OHM RESISTOR
BEFORE HANDLING.
Two quick ways to test a capacitor are a resistance and a
capacitance check. Refer to the next two figures for proper
meter connections for the resistance and capacitance test-
ing of the capacitor.
NOTE: Use a capacitor tester to check capacitance.
S-15A Resistance Check
C
AP
AC
IT
O
R
VOLT / OHM
METER
Testing Capacitor Resistance
