Lennox XP14 Elite Series Installation Instructions Manual page 23

DEFROST BOARD
DEFROST
SENSOR
HARNESS
050
APPLY GREASE BETWEEN
RETURN BEND AND SENSOR
CLIP COIL TEMP SENSORFROM
THE DEFROSTBOARD ON THE
HAIRPIN SHOWN.6fh HAIRPIN
UP ON INSIDE ROW. WIRES
ROUTED DOWN
Figure 27. Sensor Locations
Ambient Sensor--The ambient sensor (shown in figure
27) considers outdoor temperatures below -35°F (-37°C)
or above 120°F (48°C) as a fault. If the ambient sensor is
detected as being open, shorted or out of the temperature
range of the sensor, the board will not perform demand
defrost operation. The board will revert to
time/temperature defrost operation and will display the
appropriate fault code. Heating and cooling operation will
be allowed in this fault condition.
Coil Sensor--The coil temperature sensor (shown in
figure 27) considers outdoor temperatures below -35°F
(-37°C) or above 120°F (48°C) as a fault. If the coil
temperature sensor is detected as being open, shorted or
out of the temperature range of the sensor, the board will
not perform demand or time/temperature defrost
operation and will display the appropriate fault code.
Heating and cooling operation will be allowed in this fault
condition.
OPERATIONAL DESCRIPTION
The defrost control board has three basic operational
modes: normal, calibration, and defrost.
Normal Mode--The demand defrost board monitors the
O line, to determine the system operating mode
(heat/cool), outdoor ambient temperature, coil
temperature (outdoor coil) and compressor run time to
determine when a defrost cycle is required.
Calibration Mode--The board is considered uncalibrated
when power is applied to the board, after cool mode
operation, or if the coil temperature exceeds the
termination temperature when it is in heat mode.
Calibration of the board occurs after a defrost cycle to
ensure that there is no ice on the coil. During calibration,
the temperature of both the coil and the ambient sensor
are measured to establish the temperature differential
which is required to allow a defrost cycle.
Defrost Mode--The following paragraphs provide a
detailed description of the defrost system operation.
DETAILED DEFROST SYSTEM OPERATION
Defrost Cycles--The demand defrost control board
initiates a defrost cycle based on either frost detection or
time,
• Frost Detection--If the compressor runs longer than
34 minutes and the actual difference between the clear
coil and frosted coil temperatures exceeds the
maximum difference allowed by the control, a defrost
cycle will be initiated,
IMPORTANT - The demand defrost control board will
allow a greater accumulation of frost and will initiate
fewer defrost cycles than a time/temperature defrost
system.
• Time--If six hours of heating mode compressor run
time has elapsed since the last defrost cycle while the
Page 23
XP14 SERIES