60
Rev. 0
SERVICING
Ignition Control
Heat Anticipator Setting
White-Rodgers 50A55-288
.70 amps
Heatcraft HSI-2
.70 amps
GUCA / GCCA
If the anticipator current draw is unknown, then an amp
draw should be taken to determine the anticipator setting.
Use an amprobe as shown below. Wrap 10 turns of ther-
mostat wire around the stationary jaw of the amprobe and
divide the reading by 10.
10 TURNS OF
THERMOSTAT WIRE
(From "W" on thermostat)
STATIONARY JAW
OF AMPROBE
READS 4 AMPS
CURRENT DRAW
WOULD BE .4 AMPS
Checking Heating Anticipator Amp Draw
S-3C Cooling Anticipator
The cooling anticipator is a small heater (resistor) in the
thermostat. During the "OFF" cycle it heats the bimetal ele-
ment 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 anticipator
should maintain room temperature within 1 1/2 to 2 degrees
range.
The anticipator is fixed in the subbase and is not to be re-
placed. If the anticipator should fail for any reason, the sub-
base must be changed.
S-4 CHECKING TRANSFORMER AND CONTROL
CIRCUIT
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
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.
With Power On (and Door Interlock Switch Closed):
WARNING
LINE VOLTAGE NOW PRESENT.
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 volt-
age connections, fuse, splices, and blower door inter-
lock 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.
S-5 CHECKING PRIMARY LIMIT CONTROL
Furnaces using the WR50A55 or HSI-2 integrated ignition
control use a, preset nonadjustable, automatic reset Klixon
type limit control part number 201629__.
WARNING
Disconnect Electrical Power Supply:
1. Remove burner compartment door to gain access to
the primary limit control.
2. Remove low voltage wires at limit control terminals.
3. With an ohmmeter, test between these two terminals
(see limit figure below). Should read continuous unless
heat exchanger temperature is above limit control set-
ting. If not as above, replace the control.
VOLT / OHM
METER
Color
Identifing
Tab
Testing Primary Limit Control
