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 3A & 3B.
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 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
¼inch 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
¼inch 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.