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.
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.
OPTION SWITCH POSITIONS
COOL delay-
to-fan-off:
Set switch
#1
45 sec.*
90 sec.
On
Off
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.
HEAT delay-
to-fan-on:
Set switch
#2
30 sec.*
45 sec.
On
Off
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. Thiscanoccuramaximumof11timesbeforesystem
lockout.
HEAT delay-
to-fan-off:
Set switch
#3
#4
60 sec.
90 sec.
120 sec.
180 sec.*
On
Off
On
Off
On
On
Off
Off
A momentary loss of gas supply, flame blowout, or a shorted or
openconditionintheflameprobecircuitwillbesensedwithin2.0
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.
* Factory setting
HEAT MODE
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.
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.
COOL MODE
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
thecontrolgoesintoretrymode. Forthesecondattempttoignite
gaswithinthesamecallforheat,thecontrolincreasestheignitor
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.
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
circulatorfan(coolspeed)andoptionalelectronicaircleanerare
energized. When the fan switch is returned to the AUTO posi-
tion, the circulator fan and electronic air cleaner (optional) are
de-energized.
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
6