507640-05
Page 21 of 25
Issue 2245
Defrost Board Diagnostic LEDs
Green LED
(DS2)
Red LED
(DS1)
Condition
OFF
OFF
No Power to Control
Simultaneous slow FLASH
Normal Operation /
Power to Control
Alternating Slow FLASH
5-min Anti-Short-Cycle Delay
ON
Slow FLASH
Low Pressure Switch Ignored
(Low Ambient)
Fault & Lockout Codes
OFF
Slow FLASH
Low Pressure Switch Fault
OFF
ON
Low Pressure Switch Lockout
Slow FLASH
OFF
High Pressure Switch Fault
ON
OFF
High Pressure Switch Lockout
Table 4. Defrost Control (CMC1) Diagnostic LEDs
System Performance
This equipment is a self-contained, factory optimized
refrigerant system, and should not require adjustments to
system charge when properly installed. If unit performance
is questioned, perform the following checks.
Ensure unit is installed per manufacturer’s instructions and
that line voltage and air flow is correct. Refer to Table 6 and
Table 7 for proper performance value. The indoor metering
device varies by model.
If the measured performance value varies from table value
allowance, check internal seals, service panels and duct
work for air leaks, as well as restrictions and blower speed
settings. If unit performance remains questionable, remove
system charge, evacuate to 500 microns, and weigh in
refrigerant to nameplate charge. It is critical that the exact
charge is re-installed. Failure to comply will compromise
system performance.
If unit performance is still questionable, check for
refrigerant-related problems, such as blocked coil or
circuits, malfunctioning metering device or other system
components.
Gas Heating Sequence of Operation
When the thermostat calls for gas heating, R is closed to
W. The following describes the gas heating sequence of
operation.
1. A call for heat from the room thermostat starts the
combustion air blower and the circulating air blower.
2. When the speed of the combustion air blower reaches
proper RPM, the pressure switch closes, initiating a
pre-purge period (30 seconds nominal).
3. When the pre-purge period has expired, the ignition
control energizes the main gas valve and spark
electrode for a period of 10 seconds.
4.
If the flame sensor does not sense that a flame has
been established in the 10-second interval, then the
ignition control will de-energize the gas valve, and
begins a 30 second interpurge period, then initiates
another trial for ignition.
5. The ignition control is designed to repeat this “trial
for ignition” a total of three times. If, at the end of the
third trial, flame still has not been established, then the
ignition control will try to light again 1 hour later. The
1-hour retry is indefinite. The ignition control can be
reset by interrupting the unit power or the thermostat
circuit.
6.
Once flame sense has been established, the circulating
air blower is energized after a 30 seconds blower on
delay.
7.
When the thermostat is satisfied, the combustion air
blower and gas valve are de-energized. The circulation
air blower will continue to run for a short period after
the furnace is shut down.
Blower OFF Delay – Heating
The circulating air blower “OFF” delay is 120 seconds after
shutting down the burners. This delay is not adjustable.
Safety Controls
The control circuit includes the following safety controls:
Limit Control
This control is located behind the heat exchanger access
panel and is designed to open at abnormally high circulating
air temperatures. It resets automatically. The limit control
operates when a high temperature condition, caused by
inadequate airflow, occurs.
Pressure Switch
If the combustion air blower should fail, the pressure
switch prevents the spark electrode and gas valve from
being energized.
Flame Sensor
If the ignition control does not receive a signal from the
flame sensor indicating that the burners have established
flame, the gas valve closes after the 10-second trial for
ignition period.
Rollout Switch
The switch is located on the top of burner box. In the event
of a sustained main burner rollout, the rollout switch shuts
off the ignition control and closes the main gas valve. To
reset, push the button on top of the switch.