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XPG15 SERIES
DEMAND DEFROST CONTROL DIAGNOSTICS
See table 9 to determine demand defrost control operational conditions and to diagnose cause and solution to problems.
Table 9. Demand Defrost Control (A108) Diagnostic Light−Emitting Diodes
DS2
Green
DS1
Red
Condition/Code
Possible Cause(s)
Solution
OFF
OFF
Power problem
No power (24VAC) to demand defrost
control terminals
R
and
C
or demand
defrost control failure.
1
Check demand defrost control transformer power
(24VAC).
2
If power is available to demand defrost control and
light−emitting diode(s) do not light, replace demand
defrost control.
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 (place a jumper on 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/
temperature 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 demand defrost control has internal component failure. Cycle 24VAC power to
demand defrost control. If code does not clear, replace demand defrost control.
Slow
Flash
Fast
Flash
Heat Pump Inactive − Gas
Mode Active
1
Heat pump inactive mode due to out-
door temperature less than 32ºF.
2
Room thermostat temperature has
called for second stage heat (gas
furnace heat).
1
Code will reset when outdoor temperature raises
above 35ºF for a calculated time period.
2
Room thermostat demand is satisfied by furnace gas
heat.
FAULT and LOCKOUT CODES
(
Each fault adds one strike to that code’s counter; five strikes per code per room thermostat demand =
LOCKOUT)
OFF
Slow
Flash
Low Pressure Fault
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.
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.
OFF
ON
Low Pressure Lockout
Slow
Flash
OFF
High Pressure Fault
ON
OFF
High Pressure Lockout
NOTES
1. For proper operation the demand defrost control must have 24VAC between
R
(system power input) and
C
(system
common).
2. Placing a jumper on the demand defrost control’s TEST pins will not activate the heat pump out of inactive mode.
(24VAC power must be cycled to the demand defrost control to activate the heat pump out of inactive mode).
3. If the demand defrost control enters a low pressure LOCKOUT during heating mode, the outdoor unit will enter the heat
pump inactive mode. The demand defrost control will flash the low pressure code. If the room thermostat calls for Y1
heating in low pressure LOCKOUT, the demand defrost control will alternately display two codes four (4) seconds
for the low pressure LOCKOUT, and then four (4) seconds heat pump inactive − gas mode active code.
