Heat Pump: YHJD / YHJF

Re: Contactor Won't Energize

The defrost board does not energize the contactor on the outdoor unit.

• No Compressor Operation
• No Outdoor Fan Operation

► This condition is often mis-diagnosed as a Bad Defrost Board when the board is actually in a Lockout.

► There is no light on the defrost board to indicate that it is in a Lockout.

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 "C"  Black  and "R"  Red .
  • No Voltage = No Power to Air Handler, Blown Low Voltage Fuse or Bad Wiring
• Check for 24Vac between "C"  Black  and "Y"  Yellow .
  • No Voltage = No Call from Thermostat, Condensate Overflow Switch Open or Bad Wiring
• Check for 24Vac between  Gray  and  Black  at the Contactor Coil.
  • Power Present + Not Pulled-In = Bad Contactor
  • Power on "Y" + No Power at Contactor ⇒ Suspect a Pressure Switch Lockout ⇒
    • Reset the board by removing and re-attaching "R" and "Y" from the board. 
    • Jump the Test Pins on the Defrost Board and Recheck for 24VAC at the contactor.
      • Still No Power → Step 3. Check Pressure Switch Circuit

3. Check Pressure Switch Circuit

• Check for 24Vac between "C"  Black  and each Pressure Switch (PS) terminal on the defrost board.
  • Power on Both Terminals = Pressure Switches Closed → Step 5. Check Defrost Pin Selection
  • Power on 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  ow 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.
  • Correct Pin Position → Step 6. Check Contactor

6. Check Contactor

• Remove the  Gray  wire from the "M" terminal at the Defrost Board.
• Reset the board by removing and re-attaching "R" and "Y" from the board. 
• Jump the Test Pins on the Defrost Board and check for 24VAC between "C"  Black  and the "M" terminal.
  • Power Present = Bad Contactor