YMA - Outdoor Unit Starts Then Shuts Off

York Heat Pump: YMA **INCOMPLETE**

Re: Outdoor Unit Starts Then Shuts Off

The contactor on the outdoor unit pulls-in and the unit starts running, but shuts off after a short runtime.

CHECKOUT:

1. Check Line Voltage Power

• Disconnect power to the outdoor unit by pulling the service disconnect.
• Remove the outdoor unit electrical access panel.
• Look for any signs of burnt wires or controls.

2. Check Low Voltage Power

• Check for 24VAC between Common (Black) and Y (Yellow).
  • No Voltage = No Call from Thermostat, Condensate Overflow Switch Open or Bad Wiring
  • Voltage Present ⇒ Continue
• Allow the unit to start.
• Immediately when the unit stops running re-check for 24VAC between Common (Black) and Y (Yellow).
  • Power Stays On → Step 2. Check Pressure Switch
  • Power Drops Out ⇒ Check Thermostat to see if "Wait" timer has restarted.
    • Yes = Suspect Low Voltage Short
    • No = Check Condensate Overflow Switch​​​​​​​

3. Check Pressure Switch Circuit

• Check for 24Vac from Common (Black) to each Pressure Switch terminal on the defrost board.
  • Power on Both Terminals = Pressure Switches Closed → Step 5. Check Defrost Pin Selection
  • Power on Only One Terminal Only = Open Pressure Switch Circuit → Step 4. Check Pressure Switches

4. Check Pressure Switches

• There are two pressure switches wired in series to the Defrost Board:
  • High Pressure Switch = Yellow/Red Wires
  • Low Pressure Switch = Gray/Pink Wires
• Find and cut the factory wire nut which connects the (Yellow/Red) High Pressure Switch to the (Gray/Pink) Low Pressure Switch.
• Check continuity across both pressure switches.
  • High Pressure Switch Open = Bad High Pressure Switch
  • Low Pressure Switch Open ⇒ Check Refrigerant Pressure
    • Sufficient Pressure = Bad Low Pressure Switch
    • Low or No Pressure = Loss of Charge

5. Check Defrost Pin Selection

• If the defrost board has recently been changed, make sure that the defrost pin is in a numbered position.
  • A replacement defrost board will not energize the compressor contactor in the default "P" position.
• See Replacement Defrost Board article for details.