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DEFROST BOARD DIAGNOSTICS
See table 6 to determine defrost board operational conditions and to diagnose cause and solution to problems.
Table 6. 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 &
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/tem
perature 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 & 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 system.
3
Improper metering device installed or
incorrect operation of metering device.
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 & subcooling
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 measure
ments.
OFF ON
Low Pressure LOCKOUT
SLOW
Flash
OFF High Pressure Fault
ON OFF
High Pressure 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
LOCKOUT
OFF Fast
Flash
Discharge Sensor Fault The board detects open sensor or out of temperature sensor range. This fault is detected by allow
ing the unit to run for 90 seconds before checking sensor resistance. If the sensor resistance 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
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