White Rodgers 50A66-743 Manuale Utente

6

The option switches on the 50A66-743 control are used 
to determine the length of the heat delay-to-fan-off period. 
The following table shows the time periods that will result 
from the various switch positions.

60 sec.

90 sec.*

120 sec.
180 sec.

Off           Off
Off           On
On           Off
On           On

2 sec.

45 sec.*

Off
On

         

* Factory Setting

In a typical system, a call for heat is initiated by closing 
the thermostat contacts. This starts the 50A66 control’s 
heating sequence. The inducer blower and humidifier are 
energized. After a 15-second prepurge period, the 768A 
Silicon Nitride ignitor is powered.
This controller 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 special-
ly designed to operate with the 50A66’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 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 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.
If flame is detected, then lost, the 50A66 control will repeat 
the initial ignition sequence for a total of three “recycles”. 
After three unsuccessful “recycle” attempts, the control 
will go into system lockout.
If flame is established for more than 10 seconds after 
ignition, the 50A66 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 four 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 seconds. The gas valve will de-energize 
and the control will restart the ignition sequence. Recycles 
will begin and the burner will operate normally if the gas 
supply returns, or the fault condition is corrected, before 
the last ignition attempt. Otherwise, the control will go 
into system lockout.
If the control has gone into system lockout, it may be possi-
ble to reset the control by a momentary power interruption 
of ten seconds or longer. Refer to 

SYSTEM LOCKOUT, AND DIAGNOSTIC FEATURES.

In a typical system, a call for cool is initiated by closing 
the thermostat contacts. This starts the 50A66 control’s 
cooling sequence. The compressor is energized and the 
delay-to-fan-on period begins. After the delay-to-fan-on 
period ends, the circulator fan is energized at cool speed. 
The electronic air cleaner (optional) is also energized. After 
the thermostat is satisfied, the compressor is de-energized 
and the delay-to-fan-off period begins. After the delay-to-
fan-off period ends, the circulator fan and electronic air 
cleaner are de-energized.

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.