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Table 1
Defrost Control Board Diagnostic Led
LED 1
LED 2
Condition
Possible Cause(s)
Solution
OFF
OFF
Power problem
1
No power (24V) to board termi-
nals R & C.
2
Board failure.
1
Check control transformer pow-
er (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 connec-
tions at board or poor sensor
contact on coil.
3
Sensor failure.
1
Sensor function will resume
when coil temperature is be-
tween −20°F and 110°F.
2
Check sensor wiring connec-
tions at board and sensor con-
tact on coil.
3
Replace board and all sensors.
OFF
ON
Ambient sensor prob-
lem
1
Ambient temperature outside of
sensor range.
2
Faulty sensor wiring connec-
tions at board or sensor.
3
Sensor failure.
1
Sensor function will resume
when coil temperature is be-
tween −20°F and 110°F.
2
Check sensor wiring connec-
tions 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
Strike Out 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 re-
strictions. Check outdoor fan mo-
tor for proper operation.
2
Check approach, superheat &
subcooling temperatures.
3
Check system pressures Re
ON
FLASH
Low pressure switch cir-
cuit open during Y1 de-
mand
Improper refrigerant charge.
3
Improper metering device op-
eration.
3
Check system pressures. Re-
pair leaks. Replace metering de-
vice.
4
Make sure that sensor is prop-
erl positioned on coil and that
FLASH
ON
High pressure switch
circuit open during Y1
demand
4
Poor contact between coil sen-
sor and coil.
p p
erly positioned on coil and that
firm contact is established. Refer
to service manual for proper
placement.
ALTERNATING
FLASH
ALTERNATING
FLASH
5−minute delay
(Jumper test pins to
override delay)
Thermostat demand for cooling
or heat pump operation. Unit op-
erating in 5−minute anti−short−
cycle mode.
None required.
