Lennox HPXA12 SERIES - Three Phase Wiring Diagrams

Page 21
Table 9
Defrost Control Board Diagnostic Led
LED 1 LED 2 Condition Possible Cause(s) Solution
OFF OFF Power problem
1
No power (24V) to board terminals
R & C.
2
Board failure.
1
Check control transformer power
(24V).
2
If power is available and LED(s) are
unlit, replace board and all sensors.
ON ON Coil sensor problem
1
Coil temperature outside of sensor
range.
2
Faulty sensor wiring connections at
board or poor sensor contact on coil.
3
Sensor failure.
1
Sensor function will resume when
coil temperature is between −20°F
and 110°F.
2
Check sensor wiring connections at
board and sensor contact on coil.
3
Replace board and all sensors.
OFF ON Ambient sensor problem
1
Ambient temperature outside of
sensor range.
2
Faulty sensor wiring connections at
board or sensor.
3
Sensor failure.
1
Sensor function will resume when
coil temperature is between −20°F
and 110°F.
2
Check sensor wiring connections at
board and sensor.
3
Replace board and all sensors.
FLASH FLASH Normal operation
Unit operating normally or in standby
mode.
None required.
ON OFF
5−Strike pressure lockout
(Short test pins or reset
24V power to board to
override lockout)
1
Restricted air flow over indoor or
outdoor coil.
2
Improper refrigerant charge.
1
Remove any blockages or restric-
tions. Check outdoor fan motor for
proper operation.
2
Check approach, superheat & sub-
cooling temperatures
ON FLASH
Low pressure switch circuit
open during Y1 demand
Improper
refrigerant
charge
.
3
Improper metering device opera-
tion.
cooling temperatures.
3
Check system pressures. Repair
leaks. Replace metering device.
4
M k th t i l
FLASH ON
High pressure switch cir-
cuit open during Y1 de-
mand
tion
.
4
Poor contact between coil sensor
and coil.
4
Make sure that sensor is properly
positioned on coil and that firm con-
tact is established. Refer to service
manual for proper placement.
ALTERNATING
FLASH
ALTERNATING
FLASH
5−minute delay
(Jumper test pins to over-
ride delay)
Thermostat demand for cooling or
outdoor operation. Unit operating in
5−minute anti−short−cycle mode.
None required.
Demand Defrost Operation
The demand defrost control board initiates a defrost cycle based on either frost detection or time.
Frost Detection − If the compressor runs longer than 34 minutes and the actual difference between the clear coil and frosted coil temperatures exceeds
the maximum difference allowed by the control, a defrost cycle will be initiated.
IMPORTANT − The demand defrost control board will allow a greater accumulation of frost and will initiate fewer defrost cycles than a time/temperature
defrost system.
Time − If 6 hours of heating mode compressor run time has elapsed since the last defrost cycle while the coil temperature remains below 35°F (2°C),
the demand defrost control will initiate a defrost cycle.
Actuation − When the reversing valve is de−energized, the Y1 circuit is energized, and the coil temperature is below 35°F (2°C), the board logs the
compressor run time. If the board is not calibrated, a defrost cycle will be initiated after 34 minutes of heating mode compressor run time. The control
will attempt to self−calibrate after this (and all other) defrost cycle(s). Calibration success depends on stable system temperatures during the 20−minute
calibration period. If the board fails to calibrate, another defrost cycle will be initiated after 90 minutes of heating mode compressor run time. Once the
defrost board is calibrated, it will use demand defrost logic to initiate a defrost cycle. A demand defrost system initiates defrost when the difference be-
tween the clear coil and frosted coil temperatures exceeds the maximum difference allowed by the control OR after 6 hours of heating mode compressor
run time has been logged since the last defrost cycle.
Termination − The defrost cycle ends when the coil temperature exceeds the termination temperature or after 14 minutes of defrost operation. If the
defrost is terminated by the 14−minute timer, another defrost cycle will be initiated after 34 minutes of run time.
Test Mode − When Y1 is energized and 24V power is being applied to the board, a test cycle can be initiated by placing the termination temperature
jumper across the Test" pins for 2 to 5 seconds. If the jumper remains across the Test" pins longer than 5 seconds, the control will ignore the test pins
and revert to normal operation. The jumper will initiate one cycle per test.