White Rodgers 50A65-843 Operation Option Switches, Heat Mode, Cool Mode, Manual Fan On Mode

OPERATION

OPTION SWITCHES

The option switches on the 50A65-843 control are used to determine the length of the cool delay-to-fan-off, heat delay-to- fan-on and heat delay-to-fan-off periods. The following table shows the time periods that will result from the various switch positions.

OPTION SWITCH POSITIONS

COOL delay-	Set switch
to-fan-off:		#1
45 sec.*		On
90 sec.		Off
HEAT delay-	Set switch
to-fan-on:		#2
30 sec.*		On
45 sec.		Off
HEAT delay-	Set switch
to-fan-off:	#3	#4
60 sec.	On	On
90 sec.	Off	On
120 sec.	On	Off
180 sec.*	Off	Off

* Factory setting

HEAT MODE

In a typical system, a call for heat is initiated by closing the thermostat contacts. This starts the 50A65 control’s heating sequence. The inducer blower and optional humidifier are energized and the 768A silicon nitride ignitor is powered within one second.

This control has an adaptive algorithm that reduces the ignitor temperature to slightly greater than the minimum temperature required to ignite gas in each particular application. The control measures the line voltage and determines an initial ignitor temperature setting based on the measurement. After each successful ignition, the control lowers the ignitor temperature slightly for the next ignition attempt. The control continues to lower the ignitor temperature until ignition does not occur, and the control goes into retry mode. For the second attempt to ignite gas within the same call for heat, the control increases the ignitor temperature to the value it was on the third previous successful ignition. After ignition is successful, the control sets the ignition temperature at this value for the next 255 calls for heat, after which the control repeats the adaptive algorithm. The control is constantly making adjustments to the ignitor temperature to compensate for changes in the line voltage.

The 80 VAC Silicon Nitride ignitor manufactured by White- Rodgers must be used. These ignitors are specially designed to operate with the 50A65’s adaptive ignition routine to ensure the most efficient ignitor temperature.

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 circulator fan is energized at heat speed. If there is an optional electronic air cleaner on the system, the electronic air cleaner is also ener- gized. When the thermostat is satisfied, the gas valve is de- energized. After proof of flame loss, the 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 50A65 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 again. 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 50A65 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 50A65 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 11 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 2.0 seconds. The gas valve will de-energize and the control will restart the ignition sequence. A recycle will begin and the burner will operate normally if the gas supply returns, or the fault condition is corrected, before the last ignition attempt. Other- wise, 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 ten seconds or longer. Refer to SYSTEM LOCKOUT FEATURES.

COOL MODE

In a typical system, a call for cool is initiated by closing the thermostat contacts. This energizes the 50A65 control and the compressor. The cool delay-to-fan-on period begins. After the delay period ends, the optional electronic air cleaner is ener- gized, and the circulator fan is energized at cool speed. After the thermostat is satisfied, the compressor is de-energized and the cool mode 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 (cool speed) and optional electronic air cleaner are energized. When the fan switch is returned to the AUTO posi- tion, the circulator fan and electronic air cleaner (optional) are de-energized.

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