Lennox Elite XP16−024−230 Installation Instructions Manual page 32

DEMAND DEFROST CONTROL (A108) DIAGNOSTIC LEDS
The state (Off, On, Flashing) of two LEDs on the demand defrost control (DS1 [Red] and DS2 [Green]) indicate diagnostics
conditions that are described in table 10.
DS1 and DS2 System Status, Fault and Lockout Codes
DS2 DS1
Type
Green Red
OFF OFF Status
Simultaneous
Status
SLOW Flash
Alternating SLOW
Status
Flash
Simultaneous
Fault
FAST Flash
Alternating
Fault
FAST Flash
ON ON Fault
SLOW
OFF Fault
Flash
OFF ON Lockout
SLOW
OFF Fault
Flash
ON OFF Lockout
SLOW
ON Fault
Flash
FAST
ON Lockout
Flash
Fast
OFF Fault
Flash
Fast
OFF Lockout
Flash
(Each fault adds 1 strike to that code's counter; 5 strikes per code = LOCKOUT)
Table 10. Demand Defrost Control (A108) Diagnostic LEDs
Condition/Code
Power problem
Normal operation
5−minute anti−short cycle delay
Ambient Sensor Problem
Coil Sensor Problem
Demand Defrost Control
Failure
Low Pressure Fault
Low Pressure Lockout
High Pressure Fault
High Pressure Lockout
Discharge Line Temperature
Fault
Discharge Line Temperature
Lockout
Discharge Sensor Fault
Discharge Sensor Lockout
Possible Cause(s)
No power (24V) to demand
defrost control terminals R and C
or demand defrost control 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. Demand 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 24VAC
power to demand defrost control. If code does not clear, replace demand defrost
control.
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
system.
This code detects shorted sensor or high discharge temperatures. If the discharge
line temperature exceeds a temperature of 285ºF (140ºC) 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
demand defrost control will count one fault. After 5 faults, the demand defrost control
will lockout.
Page 32
Solution
1
Check control transformer power (24V).
2
If power is available to demand defrost con-
trol and LED(s) do not light, replace demand
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 subcooling
method.
3
Check system operating pressures and
compare to unit subcooling tables in this
instruction or located on unit access panel.
4
Make sure all pressure switches and sensors
to have secure connections to system to prevent
refrigerant leaks or errors in pressure and
temperature measurements.