Heat Pump: YMA

Re: Contactor Won't Energize

Thermostat calling for heating or cooling, but the contactor on the outdoor unit doesn't pull-in.

• No Compressor Operation
• No Outdoor Fan Operation

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 R (Red).
  • No Voltage = No Power to Air Handler, Blown Low Voltage Fuse or Bad Wiring
• Check for 24Vac between Common (Black) and Y (Yellow).
  • No Voltage = No Call from Thermostat, Condensate Overflow Switch Open or Bad Wiring
• Check for 24Vac across the Contactor Coil.
  • Power + Not Pulled-In = Bad Contactor
  • No Power ⇒ Jump the Test Pins on the Defrost Board and Recheck for 24VAC
    • Still No Power → Step 3. Check Pressure Switch Circuit

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.