Defrost Calibration And Defrost Mode Sequence Of Operations (All Versions) - Lennox XP25-024-230-01 Installation And Service Procedure

Heat pump control monitors mode
of operation through outdoor
ambient temperature, outdoor coil
temperature and compressor
run-time to determine when a
defrost cycle is required.
Note - No system alert codes can
be active during defrost
calibration.
Notes:
When the HP enters defrost, the thermostat runs
auxiliary heat with the HP, stopping the auxiliary
heat when defrost ends.
Demand Mode
After the initial calibration, the outdoor control
disables the defrost mode for 30-34 minutes in
order to avoid unnecessary defrosts. Beyond
this timing period, both the ambient coil
sensors are continuously monitored. If the coil
temperature is below 35°F (2°C) and the cal­
ibration delta is reached or accumulated com­
pressor run-time is more than six (6) hours, a
defrost is to be initiated.
YES
Figure 33. Defrost Calibration and Defrost Mode Sequence of Operations (All Versions)
Defrost Calibration
Coil sensor detects temperature below 35°F {2°C} during
either initial power-up, after loss of power or after cooling
mode, a sacrificial defrost is used to ensure there is a clear
coil before attempting calibration.
Coil sensor
below 35°F {2°C}
Accumulated compressor run-time while outdoor
coil temperature sensor input is below 35°F (2°C)
30-35 minutes
compressor
Initiate a defrost (Turn off outdoor fan, energize reversing
valve and increase compressor to 100% capacity). Monitor
coil temperature sensor input and accumulated defrost time.
How did defrost
terminate?
Coil temperature sensor input
reached specified defrost ter­
mination temperature as set
on outdoor control.
Calibration Attempted
(Unit Running in Heat Mode)
Calibration
Page 55
NO
YES
NO
run-time
YES
Defrost Mode
Defrost for 14 minutes without
the coil temperature sensor in­
put reaching defrost termina­
tion temperature as set on out­
door control.
NO
No attempt
to calibrate.
Continue to
accumulate
run-time.
NO
XP25