Page 8 of 15
506325-01
Issue 1734
Defrost Cycle
If the outdoor ambient conditions are such that frost forms
on the outdoor coil, the defrost control monitors the need
for, initiates, and terminates defrost cycles as necessary to
maintain system performance. The defrost control is time/
temperature initiated and temperature terminated with
a maximum defrost time (time-out) of 10 minutes. Time
between defrost cycles is preset at 60-minute intervals at
the factory, but can be field adjusted between 30, 60, or 90
minutes. To field adjust time between defrost cycles, place
defrost time plug in the proper position (see Figure 8).
Figure 7. Defrost Control
x
30
60
90
TEST
NORM
DLY
NOPS
Figure 8. Defrost Jumpers
Defrost control will initiate a defrost cycle if the time period
has elapsed and the defrost sensor sees a temperature
below freezing. At the start of a defrost cycle, the defrost
control will energize the reversing valve solenoid, shifting
the reversing valve and de-energizing the outdoor fan. The
defrost relay will also close, energizing auxiliary heat for
increased comfort during defrost. The unit will remain in
defrost until the defrost sensor has determined that the
frost has been removed from the coil or a 10-minute time
period has elapsed.
The defrost control is also equipped with a set of pins to aid
in the troubleshooting of the defrost system (see Figure 8).
The following is a brief outline of the testing of the defrost
system.
1. Defrost sensor must be closed, 32°F or below. If
temperatures are such that the switch will not close,
jumper between defrost sensor terminals on the
defrost control.
2. Start system in heating operation.
3. Jumper test pins. A 1/4” quick connect terminal
crimped onto a solid wire or brazing rod works well for
a test jumper. Closing test pins speeds up time interval
by a factor of 256.
Defrost Control Setting
Defrost Test Cycle Time
30 minutes
7 seconds
60 minutes
14 seconds
90 minutes
21 seconds
Table 4. Defrost Test Cycle Time
After closing test pins and appropriate cycle time has
elapsed, the reversing valve should shift to defrost mode
and the outdoor fan should stop. After 2 seconds of defrost
operation, the reversing valve should shift back to heating
operation and the outdoor fan should start.
Quiet Defrost Feature
The defrost control in this appliance is equipped with a
quiet defrost feature. With the jumper pin set at the DLY
position, at the start of the defrost cycle, the defrost control
will energize the reversing valve solenoid and de-energized
the outdoor fan, and de-energize the compressor circuit a
period of 10 seconds. The result is a much quieter defrost
cycle.
All units have the jumper pin set at the NORM position.
PS1 and PS2 terminals: These appliances are not
equipped with a pressure switch in the refrigeration system.
Therefore, the jumper on the NOPS pin is factory installed
and required.
