Lennox TPA036H4N4 Installation Instructions Manual page 30

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 as follows.
DS2 DS1
Green Red
Condition/Code
OFF OFF Power problem
Simultaneous Normal operation
SLOW Flash
Alternating SLOW 5−minute anti−short cycle delay Initial power up, safety trip, end of room
Flash
Simultaneous Ambient Sensor Problem
FAST Flash
Alternating Coil Sensor Problem
FAST Flash
ON ON Demand
Failure
Table 10. Demand Defrost Control (A108) Diagnostic Fault and Lockout Codes
DS2 DS1
Green Red
Condition/Code
(Each fault adds 1 strike to that code's counter; 5 strikes per code = LOCKOUT)
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
506650−01
Table 9. Demand Defrost Control (A108) Diagnostic LEDs
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.
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).
Defrost Control Indicates that demand defrost control has internal component failure. Cycle 24VAC power to de-
mand defrost control. If code does not clear, replace demand defrost control.
Possible Cause(s)
1
Restricted air flow over indoor or
outdoor coil.
2
Improper
system.
3
Improper metering device installed or
incorrect
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 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.
Solution
1
Check control transformer power (24V).
2
If power is available to demand defrost control and
LED(s) do not light, replace demand defrost control.
None required.
None required (Jumper TEST pins to override)
Solution
1
Remove any blockages or restrictions from coils
and/or fans. Check indoor and outdoor fan motor for
proper current draws.
refrigerant charge in
2
Check system charge using approach and subcooling
temperatures.
3
operation of metering 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
measurements.
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