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OPERATION
COOL delay-
to-fan-off:
Set switch
#1
COOL delay-
to-fan-off:
Set switch
#2 #3
0 sec.
80 sec.
On
Off
60 sec.
100 sec.
140 sec.
180 sec.
On Off
On On
Off On
Off Off
OPTION SWITCH POSITIONS
OPTION SWITCHES
(50A55-474 only)
The option switches on the 50A55-474 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 posi-
tions.
OPTION JUMPER
(50A55-571 only)
The option jumper on the 50A55-571 control is used to
determine the length of the cool delay-to-fan-off period.
The following table shows the time periods that will result
from the various jumper conditions.
HEAT MODE
In a typical system, a call for heat is initiated by closing the
thermostat contacts. This starts the 50A55 control’s heat-
ing 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.
Upon a call for heat, if the warm-up time has not been
locked, it will be decreased by one second. This reduction
of the ignitor on-time will continue until flame fails to be
achieved (resulting in a retry).
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 will be unlocked and set to 21 seconds. If flame is
then achieved, 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.
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 energized. When the thermo-
stat 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 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.
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 lockout.
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 sequence. This can occur a maximum
of 11 times before system lockout.
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 open condition in the flame probe circuit will be
sensed within 2.0 seconds. The gas valve will de-ener-
COOL delay-
to-fan-off:
Jumper
Condition
0 sec.
80 sec.
Installed
Clipped (open)
OPTION JUMPER CONDITION