53
Rev. 2
SYSTEM OPERATION
ABNORMAL OPERATION
(Models with White-Rodgers 50A52 Radiant Sense Igni-
tion Control)
1. Internal Control Failure. The system will lockout
2. Pressure Switch Stuck Closed. If the control senses
that the pressure switch is closed while the induced draft
blower is off, it waits until the switch opens—until then,
no heating components are energized. The probable
cause is either bad pressure switch or miswiring.
3. Pressure Switch Stuck Open. If the induced draft blower
is energized and the pressure switch does not close,
the control will keep the induced draft blower running
until the switch closes—until then, no other heating com-
ponents will be energized. The probable cause is either
disconnected hose to pressure switch, restricted vent
system, bad pressure switch or miswiring.
4. Ignitor failure. If the ignitor will not produce a heat sig-
nal within 90 seconds, the control will hold the gas valve
closed and the system will lockout. The probable cause
is either cracked ignitor, miswiring, or faulty radiant sen-
sor.
5. Flame lost within 90 seconds. If the heat signal is lost
(while the call for heat continues) from 0 to 90 seconds
after the gas valve opens, the system will retry once.
The probable cause is either the gas valve manually
closed, air in gas line, incorrect gas pressures, incor-
rect burner alignment, incorrect burner gap, faulty gas
valve, or faulty radiant sensor.
During a retry, the gas valve closes, and the induced
draft blower runs for 60 seconds. After the 60 seconds
are up, a new ignition sequence begins. The system will
only retry once. If the retry does not produce a flame
that lasts for at least 90 seconds, the furnace will lock-
out.
6. Flame lost later than 90 seconds. If the heat signal is
lost (while the call for heat continues) more than 90 sec-
onds after the gas valve opens, the system will recycle.
During a recycle, the gas valve closes, and a new igni-
tion sequence begins. No matter how many recycles
may occur, this alone will not cause the furnace to lock-
out.
7. Trip on High Limit or Auxiliary Limit. If the high limit
or auxiliary limit control opens during a heating cycle,
the gas valve closes. The induced draft blower runs, and
the air circulation blower runs at "Heating" speed. This
continues until the limit closes. (Note: Auxiliary limit is
manual reset, so it will never close on its own.) When
the limit closes, the induced draft blower shuts off im-
mediately, but the air circulation blower continues to run
for 90 seconds. After this 90 second cooldown is com-
pleted, a normal heating sequence can begin. The prob-
able cause is either low airflow due to dirty filter, dirty
coil, or restricted ductwork or blower speed set too low,
gas input set too high, faulty limit or faulty blower.
8. Interruption of Power Supply. If the line voltage power
is interrupted, the gas valve closes. It will remain closed
until line voltage power is restored and a low voltage call
for heat occurs at the room thermostat. At that time, a
new ignition sequence will begin.
9. Open Rollout Thermostat. If the rollout thermostat
opens during a heating cycle, the gas valve closes. The
induced draft blower runs, and the air circulation blower
runs at "Heating" speed (same symptoms as trip on high
limit). This will continue until the rollout thermostat is
manually reset. The probable cause is either incorrect
gas pressures, improper burner alignment, faulty orifice(s),
or restricted crossover gap(s).
OTHER ITEMS
A. Lockout (see previous Numbers 1, 4, 5). The gas valve,
ignitor, and induced draft blower are de-energized imme-
diately. (Exception: If a trip on high/auxiliary/rollout limit
is combined with a lockout, the induced blower will re-
main energized until the limit closes.) The air circulation
blower runs for 90 seconds, and then shuts off.
To manually end a lockout, interrupt the call for heat for
at least 1 second, but not more than 20 seconds.
To automatically end a lockout, wait three hours. The
control will automatically reset itself and try again.
B. Constant Fan. During normal operation, the air circula-
tion blower will continually run at "Cooling" speed as
long as power is present at terminal G. If a call for heat
occurs, the blower will continue to run at cooling speed
throughout the heating cycle.
If a trip on high/auxiliary/rollout limit occurs, the air cir-
culation blower will run at "Heating" speed. Even if power
is present at the G terminal the blower will run at heat-
ing speed until the limit closes.
C. Cooling Operation. With the thermostat in the COOL;
FAN-AUTO position, the air circulation blower will start
and stop at the same time as the compressor. No fan
time delay will occur.
D. Fan On/Off Timings are as described above. They are
not adjustable.
IMPORTANT: If the furnace frequently has to be reset, it
means that a problem exists that should be corrected.
