Defrost Control Board Diagnostic Leds - Lennox XPG20 Installation Instructions Manual

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.
DS2 DS1
Condition/Code
Green Red
OFF OFF Power problem
Simultaneous
Normal operation
SLOW Flash
Alternating SLOW 5−minute anti−short cycle
Flash delay
Simultaneous
Ambient Sensor Problem
FAST Flash
Alternating
Coil Sensor Problem
FAST Flash
ON ON Circuit Board Failure
FAULT and LOCKOUT CODES (Each fault adds 1 strike to that code's counter; 5 strikes per code = LOCKOUT)
SLOW
OFF Low Pressure Fault
Flash
Low Pressure Discharge Sen-
OFF ON
sor Lockout
SLOW
OFF High Pressure Fault
Flash
High Pressure Discharge
ON OFF
Sensor Lockout
SLOW Discharge Line Temperature
ON
Flash Fault
Discharge Line
FAST
Temperature
ON
Flash
Sensor Lockout
Fast
OFF Discharge Sensor Fault
Flash
Fast
OFF
Discharge Sensor Lockout
Flash
Table 11. Defrost Control Board Diagnostic LEDs
Possible Cause(s)
No power (24V) to board terminals R
and C or board failure.
Unit operating normally or in standby
mode.
Initial power up, safety trip, end of
room thermostat demand.
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).
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).
Indicates that board has internal component failure. Cycle 24 volt power to board. If code does
not clear, replace board.
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.
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
Discharge compressor will remain off until the discharge temperature has dropped below 225ºF (107ºC).
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.
Solution
1
Check control transformer power (24V).
2
If power is available to board and LED(s) do not
light, replace board.
None required.
None required (Jumper TEST pins to override)
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.
Page 39
XPG20 SERIES