White Rodgers 50A55-143 - Manual (Page 6)

6
OPERATION
OPTION SWITCHES
The option switches on the 50A55-143 control are used to
determine the length of the heat delay-to-fan-off periods.
The following table shows the time periods that will result
from the various switch positions.
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 after the 30-second prepurge the
ignitor is powered within one second.
This controller has an adaptive algorithm that adjusts the
duration of the ignitor warm-up, to extend ignitor life. Upon
initial application of power, the warm-up time is 17 sec-
onds. The ignitor on-time will then be increased or de-
creased 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 in 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 optional elec-
tronic air cleaner is energized and the circulator fan is
energized at heat speed. When the thermostat is satis-
fied, the gas valve is de-energized. After proof of flame
loss, the heat 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 an additional 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 four “recycles”.
After four 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 five 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-
gize and the control will restart the ignition sequence.
Recycles will begin and the burner will operate normally
if the gas supply returns, or the fault condition is corrected,
before the last ignition attempt. Otherwise, the control will
go into system lockout.
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.
HEAT delay-
to-fan-on:
Set switch
#1 #2
15 sec.
30 sec.
45 sec.
60 sec. Off Off
Off On
On Off
On On
HEAT delay-
to-fan-off:
Set switch
#3 #4
60 sec.
90 sec.
120 sec.
180 sec.
On On
Off On
On Off
Off Off
OPTION SWITCH POSITIONS