Williams 4003532 - Manual (Page 15)

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OWNER’S MANUAL
TROUBLESHOOTING
WARNING: Turn off and unplug furnace and let cool before servic-
ing. Unless you need gas supply for testing, shut off equipment shutoff
valve before servicing. Only a qualified service person should service
and repair furnace.
Continued
Note: All troubleshooting items are listed in
order of operation.
OBSERVED PROBLEM
No heat
POSSIBLE CAUSE
1. Thermostat off
2. Gas supply
3. Electrical connections and power
4. Motor
5. Malfunctioning microswitch
6. Gas valve
REMEDY
1. Check to be sure thermostat is calling for heat.
Wire to thermostat could be off terminal
2. Be sure equipment gas valve is in the open posi-
tion (level or parallel to gas line)
3. Be sure all electrical connections are secure
4. Motor must be operating at top speed before
burner will come on. If blower is not operating
at top speed, check voltage supply (minimum
100 volts A.C.). If voltage supply is okay, check
for defective motor
5. Be sure the microswitch is sailing in far enough
to open the solenoid valve and to energize the
ignition control. If the switch is not sailing in,
clean any dust or dirt from the actuator pin. Other
reasons for the switch not sailing in are
A. Insufficient blower speed - Slow motor due to
faulty motor or lint and dust accumulation on
the blower wheels or restriction of return air to
the furnace
B. Faulty microswitch - Replace switch if cir-
cuit to ignition control is not completed when
switch is manually engaged. Switch should
also be replaced if blower motor running at
top speed fails to engage switch within six or
seven seconds.
Note: To service switch, com-
bustion chamber must be pulled out. Follow
steps 1, 2, 3, 9 and 10 on page 8 to remove
combustion chamber
6. Within 20 seconds after motor reaches 75% of
its r.p.m. and microswitch engages, check the
following:
A. Voltage at valve - If current is present but
valve is not opening, check wire connections
B. If wire connections okay - Replace valve
C. No voltage at valve - Check circuit completion
through microswitch and limit switch as well
as wiring and wire connections. If no defects
are found, see Ignition Failures, page 16