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SEQUENCE OF OPERATION
COOLING STAGE 1 – Circuit R-Y makes at thermostat
pulling in compressor contactor, starting the compressor and
outdoor motor. The G (indoor motor) circuit is automatically
completed on any call for cooling operation or can be energized
by manual fan switch on subbase for constant air circulation.
COOLING STAGE 2 – Circuit R-Y1 makes at the thermostat
energizing the 2nd stage solenoid in the compressor. Default
position is not energized. Compressor will run at low capacity
until this solenoid is energized.
HEATING STAGE 1 – A 24V solenoid coil on reversing
valve controls heating cycle operation. Two thermostat options,
one allowing "Auto" changeover from cycle to cycle and the
other constantly energizing solenoid coil during heating season
and thus eliminating pressure equalization noise except during
defrost, are to be used. On "Auto" option a circuit is completed
from R-B and R-Y on each heating "on" cycle, energizing
reversing valve solenoid and pulling in compressor contactor
starting compressor and outdoor motor. R-G also make
starting indoor blower motor. Heat pump heating cycle now
in operation. The second option has no "Auto" changeover
position, but instead energizes the reversing valve solenoid
constantly whenever the system switch on subbase is placed in
"Heat" position, the "B" terminal being constantly energized
from R. A thermostat demand for Stage 1 heat completes R-Y
circuit, pulling in compressor contactor starting compressor and
outdoor motor. R-G also make starting indoor blower motor.
HEATING STAGE 2 – Circuit R-Y2 makes at the thermostat
energizing the 2nd stage solenoid in the compressor.
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. See Tables 5A & 5B.
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.
Manual 2100-586B
Page
16 of 25
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 8.
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.
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Table of Contents
Troubleshooting
