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XPG20 SERIES
Defrost Control Board Diagnostic LEDs
The state (Off, On, Flashing) of two LEDs on the DCB (DS1 [Red] and DS2 [Green]) indicate diagnostics conditions that are
described in Table 11.
Table 11. Defrost Control Board Diagnostic LEDs
DS2
Green
DS1
Red
Condition/Code
Possible Cause(s)
Solution
OFF
OFF
Power problem
No power (24V) to board terminals R
and C or board failure.
1
Check control transformer power (24V).
2
If power is available to board and LED(s) do not
light, replace board.
Simultaneous
SLOW Flash
Normal operation
Unit operating normally or in standby
mode.
None required.
Alternating SLOW
Flash
5−minute anti−short cycle
delay
Initial power up, safety trip, end of
room thermostat demand.
None required (Jumper TEST pins to override)
Simultaneous
FAST Flash
Ambient Sensor Problem
Sensor being detected open or shorted or out of temperature range. Board will revert to time/
temperature defrost operation. (System will still heat or cool).
Alternating
FAST Flash
Coil Sensor Problem
Sensor being detected open or shorted or out of temperature range. Board will not perform
demand or time/temperature defrost operation. (System will still heat or cool).
ON
ON
Circuit Board Failure
Indicates that board has internal component failure. Cycle 24 volt power to board. If code does
not clear, replace board.
FAULT and LOCKOUT CODES
(Each fault adds 1 strike to that code’s counter; 5 strikes per code = LOCKOUT)
OFF
SLOW
Flash
Low Pressure Fault
1
Restricted air flow over indoor or out-
door coil.
2
Improper refrigerant charge in sys-
tem.
3
Improper metering device installed or
incorrect operation of metering de-
vice.
4
Incorrect or improper sensor location
or connection to system.
1
Remove any blockages or restrictions from coils
and/or fans. Check indoor and outdoor fan motor for
proper current draws.
2
Check system charge using approach and subcool-
ing temperatures.
3
Check system operating pressures and compare to
unit charging charts.
4
Make sure all pressure switches and sensors have
secure connections to system to prevent refrigerant
leaks or errors in pressure and temperature mea-
surements.
OFF
ON
Low Pressure Discharge Sen-
sor Lockout
SLOW
Flash
OFF
High Pressure Fault
ON
OFF
High Pressure
Discharge
Sensor Lockout
SLOW
Flash
ON
Discharge Line Temperature
Fault
This code detects shorted sensor or high discharge temperatures. If the discharge line
temperature exceeds a temperature of 300ºF (148ºC) during compressor operation, the board
will de−energize the compressor contactor output (and the defrost output if active). The
compressor will remain off until the discharge temperature has dropped below 225ºF (107ºC).
FAST
Flash
ON
Discharge Line
Temperature
Discharge
Sensor Lockout
OFF
Fast
Flash
Discharge Sensor Fault
The board detects open sensor or out of temperature sensor range. This fault is detected by
allowing the unit to run for 90 seconds before checking sensor resistance. If the sensor resist-
ance is not within range after 90 seconds, the board will count one fault. After 5 faults, the board
will lockout.
Fast
Flash
OFF
Discharge Sensor Lockout
