Trane VRF System: Detailed Diagnostic Troubleshooting

This article provides detailed troubleshooting steps for the diagnostic error codes for the Trane VRF Outdoor and Indoor Units, as detailed in the service manual (VRF-SVM046A-EN).

Understanding Error Code Prefixes

The first letter of an error code provides context about the location and type of error:

Troubleshooting by Code

E121: Indoor Temperature Sensor Error

• Event: The indoor temperature sensor is open or shorted.
• Resolution:
  1. Check Connection: Ensure the indoor temperature sensor is securely connected to the control board. If loose, reconnect it and restart the unit.
  2. Measure Resistance: If the connection is secure, disconnect the sensor from the control board. Measure the resistance across its two terminals using a multimeter.
  3. Verify Resistance: Compare the measured resistance to the table below.
  4. Isolate Fault:
     • If the resistance value significantly deviates from the expected value, the sensor is faulty and must be replaced.
     • If the resistance value is within the expected range, the issue is likely with the main control board. Replace the control board and restart the unit.

E122 & E123: EVA IN / EVA OUT Sensor Error

• Event: The indoor unit's evaporator inlet (E122) or outlet (E123) temperature sensor is open or shorted.
• Resolution:
  1. Check Connection: Verify that the respective sensor (EVA IN or EVA OUT) is securely connected to the control board. If loose, reconnect and restart.
  2. Measure Resistance: Disconnect the sensor and measure its resistance.
  3. Verify Resistance: Compare the measurement with the resistance table provided under E121.
  4. Isolate Fault:
     • If the resistance is incorrect, replace the defective sensor.
     • If the resistance is correct, replace the main control board.

E128 & E129: EVA IN / EVA OUT Sensor Disconnected

• Event: The system detects that the EVA IN (E128) or EVA OUT (E129) sensor is disconnected or installed in the wrong location based on abnormal temperature readings during operation.
• Resolution:
  1. Inspect Physical Installation: Visually inspect the EVA IN and EVA OUT sensors. Ensure they are securely fastened to the correct pipes and their wiring is not damaged.
  2. Verify Connections: Confirm that the sensors are plugged into the correct terminals on the control board.
  3. Follow Flowchart for Sensor Test:
     • If the sensor appears disconnected, check the sensor and its connection. Restart the unit after securing it.
     • If the connection is good, measure the sensor's resistance (refer to the table under E121) to check for defects. Replace the sensor if faulty.

E135 / P703: Indoor Unit EEV Not Closing

• Event: The Electronic Expansion Valve (EEV) is not fully closing, allowing refrigerant to leak into the indoor unit. This is detected when the indoor coil temperature remains at 32°F (0°C) for over 20 minutes during cooling.
• Resolution:
  1. Check EEV Wiring: Ensure the EEV wire is properly connected to the indoor unit control board.
  2. Check Coil Connection: Verify the EEV coil is correctly seated on the main valve body.
  3. Test Coil Resistance: Measure the resistance of the coil terminals. If there is a disconnection or short circuit, replace the EEV coil.
  4. Reset and Re-test: If the above steps show no issues, reset the outdoor unit and run the test again. If the error persists, replace the entire EEV coil assembly.

E153: Float Switch Open Error

• Event: The float switch in the indoor unit's drain pan has remained open, indicating a high water level that is not draining.
• Resolution:
  1. Inspect Drain Pan: Check for water in the drain pan.
     • If water is present, reset the indoor unit power and verify the drain pump operates (listen for vibration). If the pump runs but water doesn't drain, check for blockages in the drain line. If the pump does not run, check for AC voltage at the pump. If voltage is present but the pump is inactive, replace the drain pump. If no voltage is present, replace the indoor control board.
     • If the drain pan is empty, the float switch itself may be defective. Disconnect the switch and test its continuity. If the switch is faulty, replace the float switch assembly.

E201 & E202: Communication Error (Indoor/Outdoor)

• Event: A communication failure has occurred between the indoor and outdoor units. This is often due to incorrect address settings or wiring issues.
• Resolution:
  1. Verify Address Settings: Press button K3 on the outdoor unit control board to track responding indoor units. Compare this with the actual number of installed units.
  2. Check for Duplicates: If an address is duplicated, a communication error will occur on all units sharing that address. Correct any duplicated addresses.
  3. Test Communication Line: If addresses are correct, disconnect the communication cable (F1/F2) and use an oscilloscope to check for a square wave signal (±0.7 Vdc or more).
     • If the signal is good, reconnect the indoor units one by one to identify the unit causing interference. Replace the control board of the faulty unit.
     • If the signal is bad, check the communication cable and its connections at the outdoor unit control board. If secure, replace the outdoor control board.