THGD - Not Defrosting/Outdoor Coil Frozen

York Heat Pump: THGD

Re: Not Defrosting / Frozen

The THGD models may use either a Time & Temperature or Demand Defrost control board.

CHECKOUT:

1. Check Outdoor Fan

• Inspect the outdoor unit and make sure the outdoor fan is operating normally.
  • Fan Operating → Step 2. Test Defrost Cycle
  • No Fan ⇒ Check for 230VAC to the fan motor.
    • No Power = Bad Control Board or Unit in Defrost
    • Power + No Fan = Bad Condenser Motor or Capacitor ⇒ Check Capacitor

2. Test Defrost Cycle

• Jump the TEST pins to force the unit into defrost (hold TEST pins until unit enters defrost).
  • Defrost Cycle Initiates & Terminates Normally → Step 3. Check Refrigerant Pressures
  • Unit Enters Defrost & Exits Quickly → Step 4. Check Defrost Stat
  • Unit Will Not Initiate Defrost = Bad Defrost Board or No 24VAC ⇒ Check for 24VAC between "R" and "C".

3. Check Refrigerant Pressures

• Hook-up refrigerant gauges to the pressure ports on the unit.
  • Blue --> "True Suction" Low Pressure
  • Red --> High Pressure (either refrigerant line)
• Monitor pressures as the system operates.

• Low Pressure Issues
  • Low Suction + Low Discharge + Expansion Valve Frosting = Low Refrigerant Charge or Bad O/D Expansion Valve
    • Try adding refrigerant through the Low Pressure gauge.
      • Suction and Discharge Pressures should gradually increase as refrigerant is added.
      • If the Discharge Pressure increases but the Suction Stays Low or Drops = Bad O/D Expansion Valve

4. Check Defrost Stat

• Disconnect high voltage power from the unit by pulling the service disconnect or turning the breaker off.
• Disconnect the two wires from the defrost board connected to "T-STAT".
• Test resistance of the stat.
  • Stat should Close below 30 deg. and Open above 65 deg.
  • Cold Stat + Open Contacts = Bad Defrost Stat