6
OPERATION
SYSTEM LOCKOUT AND DIAGNOSTIC FEATURES
COOL MODE
In a typical system, a call for cool is initiated by closing
the thermostat contacts. This energizes the 50A66-843
control's cooling sequence. The compressor is energized
and the delay-to-fan-on period begins. After the delay-
to-fan-on periods ends, the circulator fan is energized at
cool speed. The electronic air cleaner (optional) is also
energized. After the thermostat is satisfied, the compres-
sor is de-energized and the delay-to-fan-off period begins.
After the delay-to-fan-off period ends, the circulator fan
and electronic air cleaner (optional) are de-energized.
MANUAL FAN ON MODE
If the thermostat fan switch is moved to the ON position,
the circulator fan (heat speed) and optional electronic air
cleaner are energized. When the fan switch is returned
to the AUTO position, the circulator fan and electronic air
cleaner (optional) are de-energized.
If flame is detected, then lost, the 50A66-843 control will
repeat the initial ignition sequence for a total of three
"recycles". After three unsuccessful "recycle" attempts,
the control will go into system lockout.
If flame is established for more than 10 seconds after igni-
tion, the 50A66-843 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 four times before system lockout.
A momentary loss of gas supply, flame blowout, or a
shorted or open condition in the flame probe circuit will be
sensed within 2 seconds. The gas valve will de-energize
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 pos-
sible to reset the control by a momentary power interrup-
tion of ten seconds or longer. Refer to
PRECAUTIONARY,
SYSTEM LOCKOUT, AND DIAGNOSTIC FEATURES.
SYSTEM LOCKOUT FEATURES
When system lockout occurs, the gas valve is de-energized.
The circulator blower is energized at heat speed for some
faults, and if flame is sensed, the inducer blower is en-
ergized. The diagnostic indicator light will flash or glow
continuously to indicate system status.
(System lockout
will never override the precautionary features.)
To reset the control after system lockout, do one of
the following:
1. Interrupt the call for heat at the thermostat for at least
one second, but less than 20 seconds (if flame is sensed
with the gas valve de-energized, interrupting the call
for heat at the thermostat will
not reset the control).
2. Interrupt the 24 VAC power at the control for at least
ten seconds. You may also need to reset the flame
rollout sensor switch.
3. After one hour in lockout, the control will automatically
reset itself.
DIAGNOSTIC FEATURES
The 50A66-843 control continuously monitors its own
operation and the operation of the system. If a failure oc-
curs, the DS 1 (red) and DS 2 (green) LEDs will indicate
a failure code as shown on next page.
