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)

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.