Heat Pump - Kicks On and Off in Heating

Heat Pump

Re: Compressor Kicks On and Off in Heating

The compressor and condenser fan motor cycle on and off rapidly.

Often accompanied by burnt compressor contactor points from excessive cycling.

► The Low and High Pressure switches are wired in series with the "Y" output from the defrost board to the compressor contactor. A tripped switch will de-energize the contactor when it opens and re-energize once the switch closes. (No lockout)

Possible Causes (From Most to Least Likely):	Qty
High Pressure - Overcharged
Low Pressure - Low Refrigerant Charge
High Pressure - Low Indoor Airflow	2
Low Pressure - Bad Heating Expansion Valve

CHECKOUT:

1. Check Refrigerant Pressures

Turn off power to the outdoor unit by pulling the service disconnect or turning off the breaker.
Hook-up refrigerant gauges to the pressure ports on the unit.
- Blue --> "True Suction" Low Pressure
- Red --> High Pressure (either refrigerant line)
Re-apply power to the outdoor unit.
Start the compressor with a call for heating from the thermostat.
- Make sure the compressor and condenser fan start correctly.
  - No Fan Operation = Bad Condenser Motor/Capacitor or Bad Fan-Cycling Control
Observe refrigerant pressures as the system operates.
- Normal R-22 Pressures = 25 to 65 psig Suction, 150 to 270 psig Head.
- Normal R410A Pressures = 85 to 130 psig Suction, 200 to 400 psig Head.
  - Higher than Normal Head Pressure --> Step 2. Check High Pressure Issues
  - Lower than Normal Suction Pressure --> Step 3. Check Low Pressure Issues

2. Check High Pressure Issues

If the Head Pressure exceeds Trip Point within 1 minute:
- Suspect Bad Overcharge or No Indoor Airflow
If the Head Pressure gradually climbs to Trip Point:
- Place an insulated thermistor on the liquid line.
- Calculate Sub-Cooling = (Liquid-Line Gauge Temperature - Actual Liquid-Line Temperature)
  - Sub-Cooling > 13 deg + High Head Pressure + High Suction Pressure = Overcharged
  - Sub-Cooling > 13 deg + High Head Pressure + Low Suction Pressure = Bad O/D Expansion Valve
  - Sub-Cooling < 2 deg + High Head Pressure + High Suction Pressure = Low Indoor Airflow

3. Check Low Pressure Issues

If Suction Pressure drops below the Trip Point within 1 minute:
- Attempt to add refrigerant to the system.
  - Suction Pressure + Head Pressure Climbs = Low Refrigerant
    - A Liquid Line Sight Glass should have bubbles until proper charge is achieved..
  - Head Pressure Climbs but Suction Pressure stays low or drops = Bad O/D Expansion Valve
    - A Liquid Line Sight Glass should be clear.