Manual 2100-527E
Page
18 of 29
SEQUENCE OF OPERATION
COOLING
–
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.
HEATING
–
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 heat completes R-Y circuit, pulling in
compressor contactor starting compressor and outdoor
motor. R-G also make starting indoor blower motor.
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. 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
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 (HPC) 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 12.
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
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 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. 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.
