7
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 expires,
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 50A55-843 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 indica-
tor light will flash or glow continuously to indicate system status.
(System lockout will never override the precautionary fea-
tures.)
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 50A55-843 control continuously monitors its own operation
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 on continuously. In this
case, the entire control should be replaced, as the control
is not field-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 Open rollout switch
6 flashes, then pause 115 Volt AC power reversed/Im-
proper ground
7 flashes, then pause Low flame sense signal
Continuous flashing Flame has been sensed when
(no pause) no flame should be present (no
call for heat)
The LED will also flash once at power-up.
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of Emerson Electric Co.
