Bard PH10481 Installation Instructions Manual - page 22
Manual 2100-354F
Page
22 of 32
MIS-1191
DEFROST CYCLE
The defrost cycle is controlled by temperature and time on
the solid state heat pump control. See Figure 12.
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
sensor mounted near the bottom of the outdoor coil. Once
coil temperature reaches 30°F or below, the coil sends a
signal to the control logic of the heat pump control and the
defrost timer will start.
After 30 minutes 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 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 10 minutes.
There are three settings on the heat pump control – 30, 60
and 90 minutes. Models are shipped wired on the 60-minute
setting for greatest operating economy. If special
circumstances require a change to another time, remove wire
connected to terminal 60 and reconnect to desired terminal.
Refer to Figure 12. The manufacturer’s recommendation is
for 60-minute defrost cycles.
There is a cycle speed up jumper on the control. This can
be used to reduce the time between defrost cycle operation
without waiting for time to elapse.
Use a small screwdriver or other metallic object, or another
1/4 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 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
maximum defrost length sequence in a matter of seconds and
will automatically terminate the defrost sequence.
There is an initiate defrost jumper (sen jump) on the control
that can be used at any outdoor ambient during the heating
cycle to simulate a 0° coil temperature. This can be used to
check defrost operation of the unit without waiting for the
outdoor ambient to fall into the defrost region.
By placing a jumper across the SEN JMP terminals (a 1/4
inch QC terminal works best) the defrost sensor mounted
on the outdoor coils is shunted out and will activate the
timing circuit. This permits the defrost cycle to be checked
out in warmer weather conditions without the outdoor
temperature having to fall into the defrost region.
In order to terminate the defrost test in the
SEN JMP
jumper must be removed. If left in place too long the
compressor could stop due to the high pressure control
opening because of the high pressure condition created by
operating in the cooling mode with outdoor fan off.
Pressure will rise fairly fast as there is likely no actual frost
on the outdoor coil in this artificial test condition.
There is also a 5-minute compressor time delay function
built into the HPC. This is to
protect the compressor from
instances it is helpful to the
service technician to override or
speed up this timing period, and
shorting out the speedup terminals
for a few seconds can do this.
FIGURE 12
HEAT PUMP CONTROL BOARD