York Heat Pump: EFH

Re: Not Defrosting / Outdoor Coil Frozen

These units use a Yorkguard Demand Defrost control board.

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

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 the fan motor between the Purple and Black wires.
    • No Power = Bad Control Board or Unit in Defrost
    • Power + No Fan Operation = Bad Fan Motor or Capacitor ⇒ Check Capacitor

2. Check Defrost

• Yorkguard V
• Jump the two "TEST" pins on the outdoor unit control board.
• If the outdoor (ambient) temperature is below 50 deg. the unit should enter a defrost mode.
• Ensure that the outdoor fan shuts-off and the reversing valve switches to cooling mode.
  • Enters & Exits Defrost Normally → Step 5. Check Refrigerant Pressures
  • Enters & Exits Defrost too Quickly → Step 3. Check Liquid Line Sensor
  • Reversing Valve Does Not Switch ⇒ Check for 24VAC on the reversing valve solenoid.
    • Power + Doesn't Switch = Bad Reversing Valve
    • No Power = Bad Defrost Control or Loose Wiring

3. 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.
• Sensor Resistance
• Disconnect the two wires from the defrost board connected to "LL".
• Set the multi-meter on 200K Ohms.
• Test resistance of the sensor.
• Use Resistance Chart to determine sensed temperature.
  • If sensed temperature is more than 5 deg. higher or lower than the actual temperature = Bad Liquid Line Sensor
• Sensor Location
• It is very common for technicians to put the liquid line sensor in the wrong location (which can cause the unit to terminate defrost before the coil is thawed).
• The sensor must be located on the condenser coil side of the metering device, as close to the metering device as possible.
  • With an expansion valve, it is possible to mount the sensor between the valve and the coil distributor.
  • With an orifice, the proper location is typically where one of the distributor lines ties into a short 3/8" piece of copper at the coil.

4. 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 "OD".
• Set the multi-meter on 200K Ohms.
• Test resistance of the sensor.
• Use Resistance Chart to determine sensed temperature.
  • ​​​​​​​​​​​​​​If sensed temperature is more than 5 deg. higher or lower than the actual temperature = Bad Ambient Sensor
    • Ambient Temperature reading less than 50 deg and the board will not initiate defrost = Bad Defrost Board

5. 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 O/D Expansion Valve
  • Low Suction + Low Discharge + Clear Sight Glass + Expansion Valve Frosting = Bad O/D Expansion Valve