White Rodgers 50A55-743 Twinning Interface, System Lockout And Diagnostic Features

OPERATION

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. (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 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 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	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

The LED will also flash once at power-up.

6