The option switches on the 50A55-438 control are used to
determine the length of the cool delay-to-fan-off and heat delay-
to-fan-off periods. The following tables show the time periods
that will result from the various switch positions.
system for 5 seconds. When the purge is complete, the inducer
blower and humidifier are de-energized. After the delay-to-fan-
off period ends, the circulator fan and electronic air cleaner are
de-energized. If flame is not detected, both valves are de-
energized, the ignitor is turned off, and the 50A55 control goes
into the “retry” sequence.
The “retry” sequence provides a 60-second wait following an
unsuccessful ignition attempt (flame not detected). After this
wait, the ignition sequence is restarted with 2 seconds of ignitor
warm-up time. If this ignition attempt is unsuccessful, one more
retry will be made before the control goes into system lockout.
OPTION SWITCH POSITIONS
If flame is detected, then lost, the 50A55 control will repeat the
initial ignition sequence for a total of ten “recycles”. After ten
unsuccessful “recycle” attempts, the control will go into system
If flame is established for more than 10 seconds after ignition,
the 50A55 controller will clear the ignition attempt (or retry)
counter. If flame is lost after 10 seconds, it will restart the ignition
During burner operation, a momentary loss of power of 50
milliseconds or longer will de-energize the main gas valve.
When power is restored, the gas valve will remain de-energized
and a restart of the ignition sequence will begin immediately.
A momentary loss of gas supply, flame blowout, or a shorted or
seconds. The gas valve will de-energize and the control will
restart the ignition sequence. A recycle will begin and the burner
will operate normally if the gas supply returns, or the fault
condition is corrected, before the last ignition attempt. Other-
wise, the control will go into system lockout.
In a typical system, a call for heat is initiated by closing the
thermostat contacts. This starts the 50A55 control’s heating
sequence. The inducer blower and optional humidifier are
energized and the ignitor is powered within one second.
These controls have an adaptive algorithm that adjusts the
duration of the ignitor warm-up for the purpose of extending
ignitor life. Upon initial application of power, the warm-up time is
17 seconds. The ignitor on-time will then be increased or
decreased depending on whether or not flame is achieved. The
warm-up time is limited to a maximum of 21 seconds. During the
first 64 warm-up periods following power-up, the warm-up time
may not be less than 17 seconds.
If the control has gone into system lockout, it may be possible to
reset the control by a momentary power interruption of one
second or longer. Refer to SYSTEM LOCKOUT FEATURES.
Upon a call for heat, if the warm-up time has not been locked, it
time will continue until flame fails to be achieved (resulting in a
In a typical system, a call for cool is initiated by closing the
thermostat contacts. This energizes the 50A55 control. The
compressor and optional electronic air cleaner are energized,
and the circulator fan is energized at cool speed. After the
thermostat is satisfied, the compressor is de-energized and the
(optional) cool mode delay-to-fan-off period begins. After the
optional delay-to-fan-off period ends, the circulator fan and
electronic air cleaner (optional) are de-energized.
In the event of a retry, the warm-up time will be increased by two
seconds and locked at that duration. Once the warm-up time is
locked, it remains fixed until another call for heat results in a
retry, in which case, the warm-up time is again increased by two
seconds and remains locked.
In the event of two successive retry attempts, the warm-up time
the warm-up time will begin adapting again with the next call for
heat. If, however, this third attempt fails to achieve flame, the
control will go into system lockout.
MANUAL FAN ON MODE
If the thermostat fan switch is moved to the ON position, the
energized. When the fan switch is returned to the AUTO posi-
tion, the circulator fan and electronic air cleaner (optional) are
At the end of the ignitor warm-up time, both valves in the 36E
manifold gas valve are opened. Flame must be detected within
4 seconds. If flame is detected, the delay-to-fan-on period
begins. After the delay-to-fan-on period ends, the circulator fan
is energized at heat speed. If there is an optional electronic air
cleaner on the system, the electronic air cleaner is also ener-
gized. When the thermostat is satisfied, the gas valve is de-
energized. After proof of flame loss, the delay-to-fan-off period
begins and the inducer blower remains energized to purge the