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!
| Qty |
Possible Causes: |
| 3 |
Bad Liquid Line Sensor |
| 1 |
Bad Condenser Fan Motor |
|
Bad Fan Capacitor |
| 1 |
Bad Defrost Board |
|
Low Refrigerant Charge |
|
Bad Expansion Valve |
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.
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.
| Normal Pressure Range |
| Refrigerant |
0-30 Deg O/D |
30-50 Deg O/D |
| R410A |
- 75-100 Suction
- 250-320 Discharge
|
- 100-150 Suction
- 250-375 Discharge
|
| R-22 |
- 25-35 Suction
- 160-220 Discharge
|
- 36-65 Suction
- 170-260 Discharge
|
- 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