Manual 2100-654C
Page
21 of 34
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, thus eliminating pressure equalization
noise except during defrost, are to be used. On “Auto”
option a circuit is completed from R-B/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 covering all models can
be found on page 29. It is imperative to match the
correct pressure table to the unit by model number.
This unit employs high-flow Coremax valves instead of
the typical Shrader type valves.
WARNING! Do NOT use a Schrader valve core removal
tool with these valves. Use of such a tool could result
in eye injuries or refrigerant burns!
To change a Coremax valve without first removing the
refrigerant, a special tool is required which can be
obtained at www.fastestinc.com/en/SCCA07H. See the
replacement parts manual for replacement core part
numbers.
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
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 10 on page 23.
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 1/4" 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°F 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" QC terminal works best) the defrost sensor
mounted on the outdoor coil is shunted out and will
