Filter
Top Products
Manual 2100-455M
Page 19 of 28
DEFROST CYCLE
The defrost cycle is controlled by temperature and time on the
solid state heat pump control.
When the outdoor temperature is in the lower 40°F
temperature range or colder, the outdoor coil temperature is
32°F or below. This coil temperature is sensed by the coil
temperature sensor mounted near the bottom of the outdoor
coil. Once coil temperature reaches 30°F or below, the
coil temperature sensor sends a signal to the control logic
of the heat pump control and the defrost timer will start
accumulating run time.
After 30, 60 or 90 minutes of heat pump operation at 30°F
or below, the heat pump control will place the system in the
defrost mode.
During the defrost mode, the refrigerant cycle switches back
to the cooling cycle, the outdoor motor stops, electric heaters
are energized, and hot gas passing through the outdoor coil
melts any accumulated frost. When the temperature rises to
approximately 57°F, the coil temperature sensor will send a
signal to the heat pump control which will return the system
to heating operations automatically.
If some abnormal or temporary condition such as a high wind
causes the heat pump to have a prolonged defrost cycle, the
heat pump control will restore the system to heating operation
automatically after 8 minutes.
The heat pump defrost control board has an option of 30, 60
or 90-minute setting. By default, this unit is shipped from
the factory with the defrost time on the 60 minute pin. If
circumstances require a change to another time, remove
the wire from the 60-minute terminal and reconnect to the
desired terminal. Refer to Figure 12.
There is a cycle speed up jumper on the control. This can be
used for testing purposes to reduce the time between defrost
cycle operation without waiting for time to elapse.
Use a small screwdriver or other metallic object, or another
¼ inch QC, to short between the SPEEDUP terminals to
accelerate the HPC timer and initiate defrost.
Be careful not to touch any other terminals with the instrument
used to short the SPEEDUP terminals. It may take up to
10 seconds with the SPEEDUP terminals shorted for the
speedup to be completed and the defrost cycle to start.
As soon as the defrost cycle kicks in remove the shorting
instrument from the SPEEDUP terminals. Otherwise the
timing will remain accelerated and run through the 1-minute
minimum defrost length sequence in a matter of seconds and
will automatically terminate the defrost sequence.
120*
SW
1
SW
2 TIME (SEC)
OFF
OFF
ON
ON
OFF
ON
OFF
ON
30
60
180
MIS-2668 A
OFF
LOW PRESSURE BYPASS TIMER SWITCH
*(FACTORY SETTING 120 SECONDS)
ACCUMULATED DEFROST TIME TIMER
(FACTORY SETTING 60 MIN.)
ON
FIGURE 12 — DEFROST CONTROL BOARD