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

CHECKOUT:

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.

• 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.
  • Defrost Cycle Initiates & Terminates Normally → Step 3. Check Refrigerant Pressures
  • Unit Enters Defrost & Exits Quickly → Step 4. Check Liquid Line Sensor
  • Unit Will Not Initiate Defrost → Step 5. Check Ambient Sensor

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)