Heat pump control monitors mode of
operation through outdoor ambient
temperature (RT13), outdoor coil
temperature (RT21) and compressor
run-time to determine when a defrost
cycle is required.
NOTE — No system alert codes can
be active for defrost calibration to be
achieved.
100
E47
DEGREE
TARGET
*Heat Pump Control (A175)
Defrost Termination (E47)
Pins (Factory Default is 50ºF)
90
DEGREE
TARGET
70
DEGREE
TARGET
*50
DEGREE
TARGET
Demand Mode
After the initial calibration, the heat pump con
trol disables the defrost mode for 30-34 min
utes in order to avoid unnecessary defrosts.
Beyond this timing period, both the ambient
(RT13) and coil (RT21) sensors are continu
ously monitored. If the coil temperature is be
low 35°F (2°C) and the calibration delta is
reached or accumulated compressor run-time
is more than six (6) hours, a defrost is to be initi
ated.
XP17
Coil sensor (RT21) detects temperature below 35°F {2°C}
during either initial power-up, after loss of power or after
cooling mode, a sacrificial defrost will be used to ensure there
is a clear coil before attempting calibration.
Accumulate compressor run-time while outdoor
coil temperature sensor input (RT21) is below
35°F (2°C)
Coil temperature sensor input
(RT21) reached specified de
frost termination temperature
as set on heat pump control
E47 pins*.
Calibration Attempted
(Unit Running in Heat
Calibration
YES
Figure 32. Defrost Calibration and Mode Sequence of Operations
Defrost Calibration
Coil sensor
below 35°F {2°C}
YES
30-35 minutes
compressor
run-time
YES
Defrost Mode
Initiate a defrost and monitor coil temperature
sensor input (RT21) and accumulate defrost time.
How did defrost
terminate?
Defrosted for 14 minutes with
out the coil temperature sensor
input (RT21) reaching defrost
termination temperature as set
on heat pump control E47
pins*.
Mode)
NO
Page 55
No attempt
NO
to
calibrate.
Continue to
accumulate
NO
run time.