Abnormality of superheat due to low discharge temperature

What does U7 mean?

This fault occurs when the discharge superheat remains at or below -15˚C (5˚F) continuously for 3 minutes, even after the linear expansion valve has reached its minimum open pulse and the compressor has been operating for 10 minutes. This indicates insufficient superheat, potentially due to issues with the discharge thermistor, linear expansion valve, or refrigerant charge, which can lead to liquid refrigerant returning to the compressor, risking compressor damage.

Complete Troubleshooting Guide

1. 1

   Inspect the discharge temperature thermistor (TH4) and its holder for proper installation, secure connection, or any signs of disconnection or loose wiring.

2. 2

   Check the coil of the linear expansion valve for continuity and proper function. Also, inspect the connections of LEV-A and LEV-B on the outdoor controller circuit board. Refer to section 10-7.

3. 3

   Verify the operation of the linear expansion valve itself. If it appears defective, it may require replacement. Refer to section 10-6.