Lennox XP16 Series Unit Information page 41

DEFROST BOARD DIAGNOSTIC LEDS
The state (Off, On, Flashing) of two LEDs on the defrost board (DS1 [Red] and DS2 [Green]) indicate diagnostics conditions
that are described in table 4.
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 Circuit Board Failure
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
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
XP16
Table 4. Defrost Control Board Diagnostic LEDs
Possible Cause(s)
No power (24V) to board terminals R and
C or board failure.
Unit operating normally or in standby
mode.
thermostat demand.
Sensor being detected open or shorted or out of temperature range. Board will revert to time/temper-
ature 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 24VAC power to board. If code does not
clear, replace board.
Table 5. Defrost Control Board Diagnostic Fault and Lockout Codes
Possible Cause(s)
1
Restricted air flow over indoor or
outdoor coil.
2
Improper refrigerant charge in system.
3
Improper metering device installed or
LOCKOUT
incorrect operation of metering device.
4
Incorrect or improper sensor location
or connection to system.
LOCKOUT
This code detects shorted sensor or high discharge temperatures. If the discharge line temperature
exceeds a temperature of 285ºF (140ºC) 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 resistance 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)
Solution
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 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
measurements.
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