Lennox XP14 Elite Series Installation Instructions Manual page 23

DEFROST BOARD DIAGNOSTICS
See table 10 to determine defrost board operational conditions and to diagnose cause and solution to problems.
DS2 DS1
Condition/Code
Green Red
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 Circuit Board Failure
FAULT and LOCKOUT CODES
SLOW
OFF Low Pressure Fault
Flash
OFF ON Low Pressure LOCKOUT
SLOW
OFF High Pressure Fault
Flash
ON OFF High Pressure LOCKOUT
SLOW Discharge Line Temperature
ON
Flash Fault
Discharge Line Temperature
FAST
ON
Flash
LOCKOUT
Fast
OFF Discharge Sensor Fault
Flash
Fast Discharge Sensor
OFF
Flash
LOCKOUT
Sensor Temperature Range °F (°C)
Outdoor (Ambient) −35 to 120 (−37) to (48)
Coil −35 to 120 (−37) to (48)
Note: Sensor resistance decreases as sensed temperature increases (see figure 27).
Table 10. 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.
Initial power up, safety trip, end of
room thermostat demand.
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).
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 24 volt power to board. If code does
not clear, replace board.
(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 model does not have a defrost line sensor, therefore this code is not applicable.
The XP14 series units does not use a defrost line sensor. However, a resistor is installed
across pins P4−1 and P4−2. If the resistor is missing or damage then this fault code will be
displayed.
This model does not have a defrost line sensor, therefore this code is not applicable.
Table 11. Sensor Temperature / Resistance Range
100
5750
90
7450
80
9275
70 11775
60 15425
50 19975
26200
40
30
20
10
0
10000 30000
RESISTANCE (OHMS)
Figure 27. Ambient and Coil Sensors
Page 23
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)
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.
Resistance Values Range (ohms)
280,000 to 3750
280,000 to 3750
34375
46275
62700
85300
50000 70000 90000
Pins/Wire Color
3 and 4 (Black)
5 and 6 (Brown)
XP14 SERIES