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506586−01 10/10
Continue
to
accumulate
run
time.
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.
Defrost Calibration
Defrost Mode
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 Mode)
Calibration
Demand Mode
After the initial calibration, the heat pump control
disables the defrost mode for 30−34 minutes in
order to avoid unnecessary defrosts. Beyond
this timing period, both the ambient (RT13) and
coil (RT21) sensors are continuously moni-
tored. If the coil temperature is below 35°F (2°C)
and the calibration delta is reached or accumu-
lated compressor run−time is more than six (6)
hours, a defrost is to be initiated.
100
90
DEGREE
TARGET
70
DEGREE
TARGET
*50
DEGREE
TARGET
100
90
70
50
DEGREE
TARGET
100
90
70
50
100
90
70
50
100
90
70
50
E47
*Heat
Pump
Control
(A175)
Defrost
Termination
(E47)
Pins
(Factory
Default
is
50ºF)
Coil
sensor
below
35°F
{2°C}
No
attempt
to
calibrate.
30−35
minutes
compressor
run−time
Accumulate compressor run−time while outdoor
coil temperature sensor input (RT21) is below
35°F (2°C)
Defrosted for 14 minutes with-
out the coil temperature sensor
input (RT21) reaching defrost
termination temperature as set
on heat pump control E47
pins*.
How
did
defrost
terminate?
NO
NO
YES
YES
NO
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.
Initiate a defrost and monitor coil temperature
sensor input (RT21) and accumulate defrost time.
YES
NOTE Ċ No system alert codes can
be active for defrost calibration to be
achieved.
Figure 26. Defrost Calibration Sequence of Operations