Trane Heat Pump: 4TWR3
Re: Flashing Code 4
Code 4 = 4 trips of the Low Pressure Control
- 1st LPCO trip = 15 min. Soft lockout
- 2nd LPCO trip = 30 min. Soft Lockout
- 3rd LPCO trip = 4 hour (cooling), 18 hour (heating) Soft Lockout
- 4th LPCO trip = Hard Lockout
||Low Refrigerant Charge
||Bad Low Pressure Switch
||Bad Fan Motor
||Bad Expansion Valve
1. Reset & Check Operation
- Reset the outdoor unit by cycling 24VAC power to the defrost board.
- Make sure the compressor and outdoor fan motor restart
2. Check Refrigerant Pressures
- Hook-up refrigerant gauges to the pressure ports on the unit.
- In heating mode you should connect to the "True" suction and discharge ports behind the panel to the left of the control panel.
- Monitor pressures as the system operates.
|Normal Pressure Range
||0-30 Deg O/D
||30-50 Deg O/D
- 75-100 Suction
- 250-320 Discharge
- 100-150 Suction
- 250-375 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 Pressure + Low Discharge Pressure + 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 Pressure + Low Discharge Pressure + Clear Sight Glass + Expansion Valve Frosting = Bad Expansion Valve
3. Test Defrost Cycle
- Ensure that the Lite-Port LED is lit or flashing.
- No Light = Bad Defrost Control or No 24VAC Power ⇒ Check for 24VAC between "R" and "B". (Unit will operate but not defrost without 24V power.)
- Jump the TEST_COMMON to FRC_DFT pins to force the unit into defrost.
- Defrost Sequence
- Compressor & outdoor fan shut-off and the reversing valve energizes.
- Compressor re-starts after approx. 20 seconds (outdoor fan stays off).
- Unit stays in defrost until liquid line sensor reads 47 or 70 deg. (See Step 6. Defrost Termination Temperature)
- Outdoor fan restarts for several seconds.
- Compressor shuts-off & the reversing valve de-energizes.
- Outdoor unit restarts after approx. 20 seconds.
4. Defrost Termination Temperature
- The defrost control board has an adjustable termination temperature.
- If everything tests correctly but the unit still has defrost issues, you can increase the defrost termination temperature.
- As shipped from the factory, the termination temperature is 47 deg.
- Clipping J2 (above the Test pins) changes the termination temperature to 70 deg. (Longer defrost cycle)