Filter
Top Products
Manual 2100-511
Page 17 of 27
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-W1 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 4A & 4B.
DEFROST CYCLE
The defrost cycle is controlled by temperature and time
on the solid state heat pump control. See Figure 8.
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 8.
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. 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.