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To reset the control after system lockout, do one of
the following:
1. Interrupt the call for heat or cool 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
one second. 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 50A55-743 control continuously monitors its own op-
eration and the operation of the system. If a failure occurs,
the LED will indicate a failure code as shown below. If the
failure is internal to the control, the light will stay off.
In this case, the entire control should be replaced, as
thecontrolisnoteld-repairable.
If the sensed failure is in the system (external to the
control), the LED will flash in the following flash-pause
sequences to indicate failure status (each flash will last
approximately 0.25 seconds, and each pause will last
approximately 2 seconds).
1 flash, then pause System lockout
2 flashes, then pause Pressure switch stuck closed
3 flashes, then pause Pressure switch stuck open
4 flashes, then pause Open limit switch
5 flashes, then pause Flame has been sensed when
no flame should be present (no
call for heat)
6 flashes, then pause Open rollout switch
7 flashes, then pause Low flame sense signal
Continuous flashing 115 Volt AC power reversed
OFF Control failure
ON Normal operation
TheLEDwillalsoashonceatpower-up.
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.
TWINNING INTERFACE
If the control has six screw terminals, one of which is
designated TWIN, the control is equipped with a single
wire twinning interface. If twinning is used, either control
will process a call for heat, cool or fan as described above.
However, after the heat-, cool-, or fan-on delay time ex-
pires, both units will energize the circulator blowers at the
same time. Likewise, after the heat-, cool-, or fan-off delay
time expires, both units will de-energize the circulator
blowers at the same time. This allows for proper air flow
to be obtained. To assure proper control operation, both
controls must share a common transformer ground (TR).
To enable twinning, do the following.
1. Power supplied to both furnaces must be from the
same phase of the incoming 120 VAC power.
2. Connect the TWIN screw terminals on the 50A55-743
of the furnaces to be twinned to each other using a
single wire (14-22 AWG.).
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, and, if
flame is sensed, the inducer blower is energized. The
diagnostic indicator light will flash or glow continuously
to indicate system status. (Systemlockoutwillnever
overridetheprecautionaryfeatures.)
OPERATION