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Manual 2100-193O
Page 21 of 26
PRESSURE SERVICE PORTS
High and low pressure service ports are installed on all
units so that the system operating pressures can be
observed. Pressure tables can be found on Page 25
covering all models. It is imperative to match the
correct pressure table to the unit by model number.
DEFROST CYCLE
The defrost cycle is controlled by temperature and time
on the solid state heat pump control. See Figure 16.
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.
After 60 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 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 10 minutes.
The heat pump defrost control board has an option of 30,
60 or 90-minute setting. All models are shipped from
the factory on the 60-minute pin. If special
circumstances require a change to another time, remove
the wire from the 60 minute terminal and reconnect to
the desired terminal. The manufacturer's
recommendation is for 60 minute defrost cycles. Refer
to Figure 16.
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 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.
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 coil 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 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
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
short cycling conditions. In some
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 16
DEFROST CONTROL BOARD