White Rodgers 21D83M-843 Operation, Replacing, Option Switches, Heat Mode, Installation Procedure

TABLE 2

Type	Existing	Replacement
	Control Board	Control Board
	ACB COOL	COOL
	ACB HEAT	HEAT
	PARK M1	PARK
L1	PARK M2	PARK
	ACC	EAC
120 VAC
	120 VAC HOT	LINE
	120 VAC TX	XFMR
	HTG ACC	HUM
	ACB LOW	FAN
Neutral	Neutral 120 VAC	Neutral
120 VAC	Return (5)	120 VAC (5)
Flame Sense	E33	FS

INSTALLATION

PROCEDURE 3

REPLACING 100925-01, 100925-02,

100925-03, 17W9201, 23W5101, 30W2501, 50A66-122, 50A66-123, 69M0801 or 69M1501

1.Disconnect all electric power and shut off gas supply to the furnace.

2.Remove the access panel

3.Disconnect wiring and remove existing ignition control board.

4.Insert the replacement board into existing holes.

5.Reconnect wiring.

6.Replace access panel.

7.Restore the electrical power and gas supply. Refer to the furnace installation instructions for start-up and check-out procedures.

OPTION SWITCHES

The option switches on the 50A66-843 control are used to determine the length of the heat delay-to-fan-off and cool-delay-to-fan-off periods. The following table shows the time periods that will result from the various switch positions.

OPTION SWITCH POSITIONS

HEAT delay-	Set switch
to-fan-off:	#1	#2
60 sec.	Off	Off
90 sec.*	Off	On
120 sec.	On	Off
180 sec.	On	On

COOL delay-	Set switch
to-fan-off:	#3
2 sec.	Off
45 sec.*	On

*Factory Setting

HEAT MODE

In a typical system, a call for heat is initiated by closing the thermostat contacts. This starts the 50A66-843 control’s heating sequence.The inducer blower and humidifier are energized. After a 15-second pre-purge period, the 768A Silicon Nitride ignitor is powered.

This controller has an adaptive algorithm that reduces 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

OPERATION

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 spe- cially designed to operate with the 50A66-843's adap- tive ignition routine to ensure the most efficient ignitor temperature.

At the end of the ignitor warm-up time, both valves in the 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 and the humidifier are energized. When the thermostat is satisfied, the gas valve is de-energized. After proof of flame loss, the inducer blower remains energized to purge the system for 5 seconds and the delay-to-fan-off period begins. 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 50A66-843 control goes into the “retry” sequence.The “retry” sequence provides a 15-second wait following an unsuccessful ignition attempt (flame not detected). After this wait, the ignition sequence is restarted. If this ignition attempt is unsuccessful, three more retries will be made before the control goes into

system lockout. 5