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Manual 2100-519C
Page 34 of 42
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 later in the manual covering all
models. It is imperative to match the correct pressure table
to the unit by model number. Upper and lower service
doors must be attached to obtain proper reading.
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 30 minute pin.
If circumstances require a change to another time, remove
the wire from the 30-minute terminal and reconnect to the
desired terminal. Refer to Figure 24.
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.
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
¼ inch QC terminal works best) the defrost sensor mounted
on the outdoor coil is shunted out & 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. The board’s LED will have a fast blink
rate when in the compressor time delay. 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.
Low Pressure Switch Bypass Operation - The control has a
selectable (SW1) low pressure switch bypass set up to ignore
the low pressure switch input during the first (30, 60, 120 or
180 seconds) of “Y” operation.
After this period expires, the control will then monitor the low
pressure switch input normally to make sure that the switch is
closed during “Y” operation.
High Pressure Switch Operation - The control has a built-in
lockout system that allows the unit to have the high pressure
switch trip up to two times in one hour and only encounter a
“soft” lockout. A “soft” lockout shuts the compressor off and
waits for the pressure switch to reset, which at that point then
allows the compressor to be restarted as long as the 5-minute
short cycle timer has run out. If the high pressure switch trips
a third time within one hour, the unit is in “hard” lockout
indicating something is certainly wrong and it will not restart
itself.