Abnormal Furnace Operation - 50A50 And 50A51 - American Standard *UD Series Operation Manual

White-Rodgers
System Lockout (Loss Of Flame)
When the Control fails to detect a flame current
signal during the trial for ignition period,1 the gas
valve and ignitor will be de-energized and the retry
sequence initiated. During the retry sequence, the
induced draft motor will be energized for an inter-
purge period.1 The ignition sequence will be restarted
with an additional period1 of ignitor warm-up time
following the interpurge period. The Control will
retry the ignition sequence 2 consecutive times
(3 total) before system lockout.
IMPORTANT
IGNITION CONTROL IS POLARITY SENSITIVE.
HOT LEG OF 120 VOLT POWER SUPPLY
MUST BE CONNECTED TO THE BLACK LINE
POWER LEAD AS INDICATED ON WIRING
DIAGRAM OR IGNITION LOCKOUT WILL OCCUR.
The initial ignition sequence will be recycled, or
repeated, if the flame is sensed and then lost after
10 seconds. The Control retry counter will be reset
if the flame is sustained for longer than 10 seconds
during an ignition recycle attempt. The system will
lockout if the flame is not sustained after the 4th or 10th1
ignition recycle attempt.
A momentary loss of gas supply, flame blowout, or a
shorted or open flame sensor will be sensed
within 0.7 seconds during a normal heating cycle.
The Control will then de-energize the gas valve and
recycle the ignition sequence. As long as the call
for heat still exists, a normal heating operation
will resume if the gas supply returns or the fault
condition is corrected before the 4th or 10th1 ignition
recycle. Otherwise, the Control will go into system lockout.
When a system lockout occurs, the Control de-energizes
the gas valve, energizes the induced draft motor (low
speed on 50A51 Controls) and energizes the indoor blower
on heat speed. The diagnostic LED will begin flashing 2
times to indicate a system lockout due to loss of flame.
If a momentary (50 milliseconds, or longer) loss
of system power occurs during a normal heating
cycle, the gas valve will be de-energized. When the
power is restored, the gas valve will remain de-energized
and the ignition sequence restarted as long as the call
for heat still exists.
1 See Integrated Furnace Control Label or Timing Chart.
50A50/50A51 Fault Diagnostics
When the Control has gone into system lockout
due to loss of flame, the Control must reset before
the system will restart the heating operation. The
Control may be manually reset by setting the
thermostat system switch to OFF and then ON
again within 1 to 21 seconds or by interrupting
system power to the Control for longer than 1 second.
The 50A50 and 50A51 Series Controls automatically
reset a system lockout condition after one or two
hours.1
Pressure Switch Problem
Single-Stage Systems
When a call for heat is received and the pressure
switch contacts are sensed closed before the induced
draft motor is energized, the Control will delay energizing
the induced draft motor, stop the ignition sequence
and begin flashing the diagnostic LED 3 times to indicate
a pressure switch problem. When the pressure switch
contacts open, a normal ignition sequence will begin after
the contacts close again and the 3 flash fault will return
to steady fast flash to indicate a normal call for heat.
When a call for heat is received and the pressure
switch contacts are sensed open after the induced
draft motor is energized, the Control will not allow the
gas valve to open. The ignition sequence will be
stopped and the diagnostic LED begins flashing
3 times to indicate a pressure switch problem. If this
occurs, the problem may be induced draft motor
failure or excessive pressure against the blower outlet
and not allowing the pressure switch contacts to
close. When the pressure switch contacts close, a normal
ignition sequence will begin and the 3 flash fault will
return to a steady fast flash to indicate a normal call
for heat.
If the control senses the pressure switch contacts are
open during a normal heating cycle, the gas valve will
be de-energized to remove the flame and the system
shutdown sequence initiated, induced draft motor will
continue to run. This problem may also be due to
induced draft motor failure or high wind. The Control
will begin flashing the diagnostic LED 3 times to
indicate a pressure switch problem. When the
pressure switch contacts close, a normal ignition
sequence will begin and the 3 flash fault will return to
a steady fast flash to indicate a normal call for heat.
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