Trane Heat Pump: 4TWX8
Re: Compressor Kicks On and Off (Heating)
The compressor and condenser fan motor cycle on and off rapidly.
►The 4TWX8 models have a 2-Stage Scroll compressor.
►The 4TWX8 models uses an Electronic Expansion Valve (EEV) for superheat control.
► The High Pressure switches is wired in series with the "Yo" output from the defrost board to the compressor contactor and the Low Pressure is wired in series with Common (B). A tripped LPCO or HPCO switch will de-energize the contactor when it opens and re-energize once the switch closes. (No lockout).
| Qty |
Possible Causes: |
|
High Pressure - Overcharged |
|
Low Pressure - Low Refrigerant Charge |
|
High Pressure - Low Indoor Airflow |
|
Low Pressure - Bad Electronic Expansion Valve |
|
Low Pressure - Bad Suction Sensor |
| 1 |
Low Pressure - Bad Pressure Transducer |
CHECKOUT:
1. Check Fault Codes
- Check the EEV Control Board for any active fault codes.
- Any fault code ⇒ See Electronic Expansion Valve Issue
2. Check Refrigerant Pressures
- Start the compressor with a call for heating from the thermostat.
- Make sure the compressor and condenser fan start correctly.
- No Fan Operation = Bad Condenser Motor/Capacitor or Bad Defrost Control ⇒ Check for 230VAC going to the fan motor.
- Observe refrigerant pressures as the system operates.
| Normal Pressure Range |
| Refrigerant |
0-30 Deg O/D |
30-50 Deg O/D |
| R410A |
- 40-85 Suction
- 250-320 Discharge
|
- 100-150 Suction
- 250-375 Discharge
|
2. Check High Pressure Issues
- If the Head Pressure exceeds Trip Point within 1 minute:
- Suspect Bad Overcharge or No Indoor Airflow
- If the Head Pressure gradually climbs to Trip Point:
- Place an insulated thermistor on the liquid line.
- Calculate Sub-Cooling = (Liquid-Line Gauge Temperature - Actual Liquid-Line Temperature)
- Sub-Cooling > 15 deg + High Head Pressure + High Suction Pressure = Overcharged
- Sub-Cooling > 15 deg + High Head Pressure + Low Suction Pressure = Electronic Expansion Valve Issue
- Sub-Cooling < 2 deg + High Head Pressure + High Suction Pressure = Low Indoor Airflow
3. Check 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 = Electronic Expansion Valve Issue
- Low Suction + Low Discharge + Clear Sight Glass + Expansion Valve Frosting = Electronic Expansion Valve Issue