30
9.4.1-
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
i
gnition 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.
9.4.2-
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
delay-to-fan off period ends, the circulator fan and electronic air cleaner
(optional) are de-energized.
9.4.3-
Manual fan on mode
If the thermostat fan switch is moved to the ON position, the circulator fan
(cool 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.
9.4.4-
Twinning interface
If the control has six screw terminals, one of which is designated TWIN,
the control is equipped with a single wire twinning interface. If twinning is
used, either control will process a call for heat, cool or fan as described
above. However, after the heat, cool, or fan-on delay time expires, both
units will energize the circulator blowers at the same time. Likewise, after
the heat, cool, or fan-off delay time expires, both units will de-energize the
circulator blowers at the same time. This allows for proper air flow to be
obtained.
To assure proper control operation, both controls must share a common
transformer ground (TR).
To enable twinning, do the following.
1.
Power supplied to both furnaces must be from the same phase of
the incoming 120 VAC power.
2.
Connect the TWIN screw terminals on the 50A55-843 of the
furnaces to be twinned to each other using a single wire (14-22
AWG.).
9.4.5-
System lockout and diagnostic features
9.4.6-
System lockout features
When system lockout occurs, the gas valve is de-energized, the circulator
blower is energized at heat speed, and, if flame is sensed, the inducer
blower is energized. The diagnostic indicator light will flash or glow
continuously to indicate system status. (System lockout will never override
the precautionary features.)
To reset the control after system lockout,
do one of the following:
1.
Interrupt the call for heat or cool at the thermostat for at least one
second but less than 20 seconds (if flame is sensed with the gas
valve de-energized, interrupting the call for heat at the thermostat
will not reset the control).
2.
Interrupt the 24 VAC power at the control for at least one second.
You may also need to reset the flame rollout sensor switch.
3.
After one hour in lockout, the control will automatically reset itself.
9.4.7-
Diagnostic features
The 50A55-843 control continuously monitors its own operation and the
operation of the system. If a failure occurs, the LED will indicate a failure
code as shown below.
If the failure is internal to the control, the light
will stay on continuously. In this case, the entire control should be
replaced, as the control is not field-repairable
.
If the sensed failure is in the system (external to the control), the LED will
flash in the following flash-pause sequences to indicate failure status
(each flash will last approximately 0.25 seconds, and each pause will last
approximately 2 seconds).
1 flash, then pause
System lockout
2 flashes, then pause
Pressure switch stuck closed
3 flashes, then pause
Pressure switch stuck open
4 flashes, then pause
Open limit switch
5 flashes, then pause
Open rollout switch
6 flashes, then pause
115 Volt AC power reversed/Improper
ground
7 flashes, then pause
Low flame sense signal
Continuous flashing
no pause)
Flame has been sensed when no
flame should be present (no call for
heat)
The LED will also flash once at power-up.
9.5- OPTION SWITCHES
– 2 STAGE, PSC
Option switches on the 50M51-843 control are used to determine the
length of the delay-to-fan-off periods. The following tables show the time
periods that will result from the various switch positions.
When using a single stage thermostat, second stage delay is based on
the setting of switch S1-1, S1-2 shown below.
Summary of Contents for c105-1-d
Page 20: ...20 Figure 16 Wiring diagram One stage PSC ...
Page 21: ...21 Figure 17 Two Stage PSC Furnace Control ...
Page 22: ...22 Figure 18 Two Stage ECM Furnace Control ...
Page 26: ...26 Figure 21 Direct venting Figure 22 Multi venting ...
Page 37: ...37 Figure 25 Part list 1 Stage PSC ...
Page 38: ...38 Figure 26 Part list 1 Stage PSC continued ...
Page 41: ...41 Figure 27 Part list 2 Stage PSC ...
Page 42: ...42 Figure 28 Part list 2 stage PCS continued ...
Page 45: ...45 Figure 29 Part list X13 ...
Page 46: ...46 Figure 30 Part list X13 continued ...
Page 49: ...49 Figure 31 Part list 2 Stage ECM ...
Page 50: ...50 Figure 32 Part list 2 Stage ECM continued ...
