York Heat Pump: BHQ

Re: Not Defrosting / Frozen

• The BHQ units have three control boards (CFM Board, Heater Board & a Demand Defrost control board).
• The Defrost Board uses an Ambient (outdoor) Sensor and Liquid Line Sensor to determine the proper conditions for defrost to occur.

CHECKOUT:

1. Check Contactor 

• Check for 24VAC across the contactor coil.
  • No Power + Unit Running = Stuck Contactor

2. Check Outdoor Fan

• Inspect the outdoor unit and make sure the outdoor fan is operating.
  • Fan Operating → Step 3. Test Defrost Cycle
  • No Fan ⇒ Check for 230VAC to fan motor on connector plug between Red and Black wires.
    • No Power = Bad Control Board or Unit in Defrost

3. Test Defrost Cycle

• At the Defrost Board jump the TEST pins to force the unit into defrost.
  • Defrost Cycle Initiates Normally → Step 4. Check Refrigerant Pressures
  • Unit Enters Defrost & Exits Quickly → Step 5. Check Liquid Line Sensor
  • Unit Will Not Initiate Defrost → Step 6. Check Ambient Sensor

4. Check Refrigerant Pressures

• Hook-up refrigerant gauges to the pressure ports on the unit.
  • Blue ⇔ Low Pressure
  • Red ⇔ High Pressure 
• Monitor pressures as the system operates.

• Low Pressure Issues
  • Low Suction + Low Discharge + Bubbles in Sight Glass + Expansion Valve Frosting = Low Refrigerant Charge
    • 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 Expansion Valve

5. Check Liquid Line Sensor

• Disconnect high voltage power from the unit by pulling the service disconnect or turning the breaker off.
• Disconnect low voltage from the defrost board by removing the Red, "R" wire.
• Disconnect the two wires from the defrost board connected to "COIL" and "COIL G".
• Set the multi-meter on 200K Ohms.
• Test resistance of the sensor.
• Use Resistance Chart to determine sensed temperature.
• Compare sensed temperature to actual temperature.
  • If sensed temperature is more than 5 deg. higher or lower than actual temperature = Bad Liquid Line Sensor

6. Check Ambient Sensor

• Disconnect high voltage power from the unit by pulling the service disconnect or turning the breaker off.
• Disconnect low voltage from the defrost board by removing the Red, "R" wire.
• Disconnect the two wires from the defrost board connected to "AMBIENT" and "AMB G".
• Set the multi-meter on 200K Ohms.
• Test resistance of the sensor.
• Use Resistance Chart to determine sensed temperature.
• Compare sensed temperature to actual temperature.
  • If sensed temperature is more than 5 deg. higher or lower than actual temperature = Bad Ambient Sensor
  • Ambient Temperature reading less than 50 deg and the board will not initiate defrost = Bad Defrost Board