Page 55
XP25
Continue to
accumulate
run-time.
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.
Defrost Calibration
Defrost Mode
Coil temperature sensor input
reached specified defrost ter
mination temperature as set
on outdoor control.
Calibration Attempted
(Unit Running in Heat Mode)
Calibration
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.
Coil sensor
below 35°F {2°C}
No attempt
to calibrate.
30-35 minutes
compressor
run-time
Accumulated compressor run-time while outdoor
coil temperature sensor input is below 35°F (2°C)
Defrost for 14 minutes without
the coil temperature sensor in
put reaching defrost termina
tion temperature as set on out
door control.
How did defrost
terminate?
NO
NO
YES
YES
NO
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.
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.
YES
Notes:
When the HP enters defrost, the thermostat runs
auxiliary heat with the HP, stopping the auxiliary
heat when defrost ends.
NO
Figure 33. Defrost Calibration and Defrost Mode Sequence of Operations (All Versions)
