York Heat Pump - Not Defrosting / Frozen

York Heat Pump: YMA

Re: Not Defrosting / Frozen

These units use a Demand Defrost control board.

The board uses an Ambient (outdoor) Sensor and Liquid Line Sensor to determine the proper conditions for defrost to occur.

♦ VERY IMPORTANT! The YMA heat pump was originally produced with R-22 refrigerant, then switched to R410a. CHECK THE NAMEPLATE BEFORE ADJUSTING CHARGE!

CHECKOUT:

1. Check Outdoor Fan

• Inspect the outdoor unit and make sure the outdoor fan is operating.
  • Fan Operating → Step 2. 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

2. Test Defrost Cycle

• Jump the TEST pins to force the unit into defrost.
  • Defrost Cycle Initiates Normally →  Step 3. Check Refrigerant Pressures
  • Unit Enters Defrost & Exits Quickly →  Step 4. Check Liquid Line Sensor
  • Unit Will Not Initiate Defrost →  Step 5. Check Ambient Sensor

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.

• If a Liquid-Line Sight Glass is installed, observe for bubbles in the sight glass (after the system has been operating for at least 5 min.)
  • Bubbles = Low Refrigerant Charge
• 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
  • Low Suction + Low Discharge + Clear Sight Glass + Expansion Valve Frosting = Bad Expansion Valve 

4. 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

5. 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