York Heat Pump: YHJF24 - 48

Re: Not Defrosting / Frozen

The YHJF 2 to 4 Ton models use a Demand Defrost control board (the 5 Ton model uses a Yorkguard VI)

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

CHECKOUT:

1. Check Contactor 

• If the outdoor unit is not operating → Step 2. Check Outdoor Fan
• If the outdoor unit is running, check for 24VAC across the contactor coil.
  • No Power + Unit Running = Stuck Contactor

2. Check Outdoor Fan

• If the outdoor unit is not operating, set the thermostat to call for heat.
• 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 the connector plug between Red and Black wires.
    • No Power = Bad Defrost Board or Unit in Defrost
    • Power Present + No Fan = Bad Condenser Fan Motor or Bad Capacitor ⇒ Test Capacitor

3. Test Defrost Cycle

• 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 ⇒ "True Suction" Port (Not the Suction Line)
  • Red ⇒ High Pressure (Liquid Line)
• Monitor pressures as the system operates.
• DO NOT ATTEMPT TO ADD FREON WHILE THE COIL IS FROZEN!

DEFROST MODE

• Connect a thermometer to the liquid line near the outdoor unit.
• Initiate a Defrost Cycle by jumping the TEST pins.
• Monitor system pressures and the liquid line temperature while the unit is in a defrost cycle.
• Suction and Discharge pressure should slowly climb as the liquid line warms.
  • Suction Pressure, Discharge Pressure and Liquid Line Temperature Don't Increase ⇒ Check Heating Mode pressures (below)

HEATING MODE

• 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 + Normal to High Discharge + Clear Sight Glass + Expansion Valve Frosting = Bad O/D 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  Blue  wires from the defrost board connected to "COIL" and "COIL G".
• Set the multi-meter on 200K (not 200) 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
  • If sensor reads correct but terminates defrost too soon ⇒ Look for Mis-Placed Coil Sensor
    • Sensor must be between the O/D Expansion Valve and the Condenser Coil on one of the feeder lines (typically a short stub of 3/8" pipe at the coil).

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  White  wires from the defrost board connected to "AMBIENT" and "AMB G".
• Set the multi-meter on 200K (not 200) 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