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DEFROST CONTROL (A108) CALIBRATION MODE SEQUENCE
Occurs after power up and cooling operation, or if the coil temperature exceeds
the termination temperature while in Heat Mode.
Demand defrost control defaults to 30 minute Ċ Time / Temperature Mode
Reset Compressor Runtime / Reset Three / Five Strike Counter
DEMAND MODE
Accumulate compressor runtime of
more than 30 minutes while coil
temperature is below 35° F (2°C).
When the accumulated compressor
time exceeds six (6) hours or if the
coil sensor indicates frost is present
on coil, go to Defrost.
THIRTY (30) MINUTE TIME /
TEMPERATURE MODE
Accumulate compressor runtime
while coil temperature is below 35° F
(2°C). When the accumulated
compressor time exceeds 30 minutes
go to Defrost.
45 MINUTE
TIME/TEMPERATURE MODE
Accumulate compressor runtime
while coil temperature is below 35°
F (2°C). When the accumulated
compressor time exceeds 45
minutes go to Defrost.
DEFROST
S Outdoor Fan OFF
S Reversing Valve ON
S W1 line ON
Monitor coil temperature and
time in defrost mode.
HOW DID DEFROST TERMINATE?
Coil temperature was above 35°F (2°C) for four (4)
minutes. of the 14−minute defrost OR reached
defrost termination temperature.
Defrosted for 14−minute without the coil temperature
going above 35°F (2°C) for four (4) minutes and coil
did not reach termination temperature.
Attempt to Calibration Ċ Temperature measurements are not taken for the first few minutes of each heat demand. This is
to allow coil temperatures to stabilize. demand defrost control has a maximum of 20 minutes of accumulated compressor
runtime in heat mode to calibrate demand defrost control This may involve more than one heating demand.
Was stable coil temperature attained
within 20 minutes?
NO Ċ Demand defrost control
reverts to 45 minute time /
temperature.
DEFROST TERMINATION
S Compressor runtime counter RESET
S Outdoor Fan ON
S Reversing Valve OFF
S W1 line OFF
DEFROST TERMINATION
S Compressor runtime counter RESET
S Outdoor Fan ON
S Reversing Valve OFF
S W1 line OFF
YES Ċ Calibration occurred
Figure 26. Defrost Calibration