Lennox Merit Series 14HPX Installation Instructions Manual page 26

DEFROST BOARD DIAGNOSTICS
See table 13 to determine defrost board operational conditions and to diagnose cause and solution to problems.
DS2 DS1
Green Red
Condition/Code
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 & LOCKOUT CODES
OFF SLOW Low Pressure Fault
Flash
OFF ON
Low Pressure
SLOW OFF High Pressure Fault
Flash
ON OFF
High Pressure
SLOW ON Discharge Line Temperature
Flash Fault
FAST ON Discharge Line Temperature
Flash LOCKOUT
OFF Fast Discharge Sensor Fault
Flash
Fast OFF Discharge Sensor
Flash LOCKOUT
Maintenance
DEALER
WARNING
Electric shock hazard. Can cause injury
or death. Before attempting to perform
any service or maintenance, turn the
electrical power to unit OFF at disconnect
switch(es). Unit may have multiple power
supplies.
506377−01 11/09
Table 13. Defrost Control Board Diagnostic LEDs
Possible Cause(s)
No power (24V) to board terminals R
& 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.
(
Each fault adds 1 strike to that code's counter; 5 strikes per code = LOCKOUT)
1
Restricted air flow over indoor or out-
door coil.
2
Improper refrigerant charge in sys-
tem.
LOCKOUT
3
Improper metering device installed or
incorrect operation of metering de-
vice.
4
Incorrect or improper sensor location
or connection to system.
LOCKOUT
This code detects shorted sensor or high discharge temperatures. If the discharge line temper-
ature 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).
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 & 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 mea-
surements.
Improper installation, adjustment, alteration, service or
maintenance can cause personal injury, loss of life, or
damage to property.
Installation and service must be performed by a licensed
professional installer (or equivalent) or a service agency.
Maintenance and service must be performed by a qualified
installer or service agency. At the beginning of each
cooling season, the system should be checked as follows:
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WARNING