28
1. Remove the burner compartment control access door.
2. IMPORTANT: Be sure that the manual gas control has been in
the “OFF” position for at least five minutes. Do not attempt to
manually light the main burners.
3. Set the room thermostat to its lowest setting and turn off the
furnace electrical power.
4. Turn the gas control knob to the “ON” position.
5. Replace the burner compartment control access door.
Failure to replace the burner door can cause products of combustion
to be released into the conditioned area resulting in personal injury or
death.
6. Turn on the manual gas stop.
7. Turn on the furnace electrical power.
8. Put thermostat to “Heat” mode and set the room thermostat at
least 10°F above room temperature to light the main burners.
9. After the burners are lit, set the room thermostat to a desired
temperature.UNIT OPERATION HAZARD
These furnaces are equipped with a manual reset limit switch in burner
assembly. This switch opens and shuts off power to the gas valve if an
overheat condition (flame rollout) occurs in burner assembly. Correct
inadequate combustion-air supply or improper venting condition before
resetting switch. DO NOT jumper this switch.
Before operating furnace, check flame rollout manual reset switch for
continuity. If necessary, press de button to reset switch. EAC-1 terminal is
energized whenever blower operates. HUM terminal is only energized
when blower is energized in heating.
8.3- SETUP SWITCHES
The furnace control has setup switches that may be set to meet the
application requirements. To set these setup switches for the appropriate
requirement:
1. Turn off electrical power.
2. Remove upper door.
3. Locate setup switches on furnace control.
4. Configure the set-up switches as necessary for the application.
5. Replace upper door and turn on electrical power.
8.4- OPTION SWITCHES – 1 STAGE, PSC
The option switches on the 50A55-843 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.
Table 15: Option switches positions
* Factory setting
8.4.1- Heat mode
In a typical system, a call for heat is initiated by closing the thermostat
contacts. This starts the 50A55 control’s heating sequence. The inducer
blower and optional humidifier are energized and the igniter is powered
within one second. This controller has an adaptive algorithm that adjusts
the duration of the igniter warm-up, to extend igniter life. Upon initial
application of power, the warm-up time is 17 seconds. The igniter on-time
will then be increased or decreased depending on whether or not flame is
achieved. The warm-up time is limited to a maximum of 21 seconds.
During the first 64 warm-up periods following power-up, the warm-up time
may not be less than 17 seconds.
Upon a call for heat, if the warm-up time has not been locked, it will be
decreased by one second. This reduction of the igniter on time will
continue until flame fails to be achieved (resulting in a retry).
In the event of a retry, the warm-up time will be increased by two seconds
and locked in at that duration. Once the warm-up time is locked, it remains
fixed until another call for heat results in a retry, in which case the warm-
up time is again increased by two seconds and remains locked.
In the event of two successive retry attempts, the warm-up time will be
unlocked and set to 21 seconds. If flame is then achieved, the warm-up
time will begin adapting again with the next call for heat. If, however, this
third attempt fails to achieve flame, the control will go into system lockout.
At the end of the igniter 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 optional electronic air cleaner is energized and the
circulator fan is energized at heat speed. When the thermostat is satisfied,
the gas valve is de-energized. After proof of flame loss, the heat delay-to-
fan-off period begins and the inducer blower remains energized to purge
the system for 15 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 igniter is turned
off, and the 50A55 control goes into the “retry” sequence. The “retry”
sequence provides a 60 seconds wait following an unsuccessful ignition
attempt (flame not detected). After this wait, the ignition sequence is
restarted with an additional 2 seconds of igniter warm-up time. 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 50A55 control will repeat the initial
ignition sequence for a total of four “recycle”. After four unsuccessful
“recycle” attempts, the control will go into system lockout.
If flame is established for more than 10 seconds after ignition, the 50A55
controller will clear the ignition attempt (or retry) counter. If flame is lost
after 10 seconds, it will restart the ignition sequence. This may 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
2.0 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 possible to reset
the control by a momentary power interruption of one second or longer.
Refer to SYSTEM LOCKOUT FEATURES.
8.4.2- Cool mode
In a typical system, a call for cool is initiated by closing the thermostat
contacts. This energizes the 50A55 control and the compressor. The cool
delay-to-fan-on period begins. After the delay period ends, the optional
electronic air cleaner is energized, 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
To Next Page