Williams 6508632 - Page 28

Troubleshooting
28
SYMPTOM
POSSIBLE CAUSE
CORRECTIVE ACTION
room temperature is
attained.
B. Defective thermostat.
Check thermostat calibration or replace.
7. Furnace operates but
will not shut "OFF"
when room
temperature is
attained.
A. Thermostat wiring
defective.
Check thermostat wiring from furnace to thermostat - may be shorted together by a
nail or staple.
B. Thermostat location.
Check thermostat location - if on an outside wall or there is a hole in wall behind the
thermostat causing cold air to contact thermostat, relocate the thermostat.
C. Improper thermostat
anticipator setting.
Set anticipator per THERMOSTAT ANTICIPATOR, page 20.
8. Abnormal operation.
A. Blower noise.
Check motor mounts - they may be loose. Blower wheel could be out of balance. Set
screw may be loose on motor shaft. Blower may be rubbing on fan shroud. Motor may
need oiling. Correct as needed.
B. Expansion noise ticking.
Check installation - casing may be twisted or not level at time of installation causing
combustion chamber to bind on its locating pins.
C. Burner resonance.
Usually associated with L.P. Gas operation. Adjust primary air screw in throat of each
cast iron burner after about 10 minutes of operation. Adjust to obtain a soft blue flame
without streaming yellow tips.
D. Selector switch defective
(2-speed).
During normal furnace operation the motor will be on "LOW" speed when operating on
minimum input capacity and on "HIGH" speed when operating at maximum input
capacity. If there is no change in motor speed, replace selector switch.
FOR MODELS: 3508231; 3508232; 5508231; 5508232
*Also applicable to Models equipped with an electric intermittent pilot system. (Continued on next page)
SYMPTOM
POSSIBLE CAUSE
CORRECTIVE ACTION
1. No spark – no pilot
gas.
A. No main power.
Perform normal system checks of main power, transformer, thermostat, limit switch,
and replace faulty component.
With power ON, turn thermostat to the lowest setting, wait for 10 seconds and return to
HIGH setting. With power ON and thermostat set at its highest position, set voltmeter
to 24V scale and attach probes to terminals "TR" and "TH" on the ignition control unit.
If you read 24V and there still is no spark or pilot gas, the ignition control is defective
and must be replaced.
B. Faulty transformer.
C. Faulty thermostat.
D. Faulty limit switch.
E. Faulty ignition control.
F. Faulty wiring.
Test wiring. Repair or replace.
G. Vent safety shutoff
device.
Check wiring connections from valve to vent safety shutoff device, be sure all
connections are tight. Check for blocked vent.
2. Spark – but no pilot
gas.
A. Faulty ignition.
See 1E.
B. No gas supplied to pilot
valve.
Check for availability of gas at gas control. Make sure the manual valve (gas cock) on
the gas control are in the full ON position.
No pilot gas could be caused by plugged pilot tubing. Also check the pilot
adjustment at the gas control.
C. Manual valves in OFF
position.
D. Faulty pilot valve.
E. Faulty wiring.
See 1F.
F. Restricted pilot line or
clogged pilot orifice.
See 2B.
3. Pilot gas – but no
spark.
A. Faulty ignition control.
With power ON, turn the thermostat to the lowest setting, wait for 10 seconds and then
return it to the high setting. With power ON and thermostat set at its highest position,
set voltmeter to 24V scale and attach probes to terminals "24V" (*TH) and "GRD"
(*TR) on the ignition control unit. If you read 24V and there is still no spark or pilot
gas, the ignition control is defective and must be replaced.
With thermostat turned to its highest setting, set test meter to 24V scale.
Touch probes to "PV/MV" and "P\/" terminals on Gas Valve. If you do not get a
24V reading, check wiring. If wiring tests okay, check ignition control.
Connect probes to "PV/MV" AND "PV" terminals on ignition control. If you do not
read 24V, the ignition control must be replaced.