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HEAT delay-
to-fan-off:
Set switch
#1 #2
180 sec.
120 sec.
90 sec.
60 sec.*
On On
On Off
Off On
Off Off
OPTION SWITCH POSITIONS
* Factory setting
OPERATION
OPTION SWITCHES
The option switches on the 50A62-820 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.
HEAT MODE
In a typical system, a call for heat is initiated by closing the
thermostat contacts. This starts the 50A62 control’s heat-
ing sequence. The inducer blower and humidifier are
energized (if there is an optional electronic air cleaner on
the system, the humidifier is not energized until the
electronic air cleaner is energized). The 768A Silicon
Nitride ignitor is powered within one second.
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 previ-
ous 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 50A62’s adaptive
ignition routine to ensure the most efficient ignitor tem-
perature.
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. When the purge is complete,
the inducer blower and humidifier are 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 flame is not detected, both valves are de-energized, the
ignitor is turned off, and the 50A62 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, one
more retry will be made before the control goes into
system lockout.
If flame is detected, then lost, the 50A62 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 50A62 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 five times before system lockout.
During burner operation, a momentary loss of power of 50
milliseconds or longer will de-energize the main gas
valve. When power is restored, the gas valve will remain
de-energized and a restart of the ignition sequence will
begin immediately.
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. Re-
cycles 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
possible to reset the control by a momentary power
interruption of one second or longer. Refer to PRECAU-
TIONARY, SYSTEM LOCKOUT, AND DIAGNOSTIC
FEATURES.
COOL MODE
In a typical system, a call for cool is initiated by closing the
thermostat contacts. This starts the 50A62 control’s cool-
ing sequence. The compressor is energized and the cool
mode 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 ener-
gized. 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 circula-
tor fan and electronic air cleaner (optional) are de-ener-
gized.