Lennox Merit 14HPX Installation Instructions Manual page 32

DEMAND DEFROST CONTROL DIAGNOSTICS
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 Demand Defrost Control
Failure
FAULT & LOCKOUT CODES
OFF SLOW Low Pressure Fault
Flash
OFF ON Low Pressure Lockout
SLOW OFF High Pressure Fault
Flash
ON OFF High Pressure Lockout
SLOW ON Discharge Line Temperature
Flash Fault
FAST ON Discharge Line Temperature
Flash Lockout
OFF Fast Discharge Sensor Fault
Flash
Fast OFF Discharge Sensor Lockout
Flash
506649−01
Table 8. Demand Defrost Control Diagnostic LEDs
Possible Cause(s)
No power (24V) to demand defrost
control terminals R & C or defrost con-
trol 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. Defrost control will revert
to time/temperature defrost operation. (System will still heat or cool).
Sensor being detected open or shorted or out of temperature range. Demand defrost control will
not perform demand or time/temperature defrost operation. (System will still heat or cool).
Indicates that demand defrost control has internal component failure. Cycle 24 volt power to
defrost control. If code does not clear, replace defrost control.
(
Each fault adds 1 strike to that code's counter; 5 strikes per code = LOCKOUT)
1
Restricted air flow over indoor or
outdoor 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.
This code detects shorted sensor or high discharge temperatures. If the discharge line
temperature exceeds a temperature of 300ºF (148ºC) during compressor operation, the
demand defrost control 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 demand defrost control 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 resistance is not within range after 90 seconds, the defrost control will count one fault.
After 5 faults, the defrost control will lockout.
Solution
1
Check control transformer power (24V).
2
If power is available to defrost control and LED(s) do
not light, replace defrost control.
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.
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