Abnormal low pressure (Low-pressure switch activated)

What does UL mean?

The 63L low-pressure switch activates, indicating system pressure below -0.07 MPa (-10 PSIG) during compressor operation. This critical fault suggests a closed outdoor unit stop valve, significant refrigerant leakage/shortage, or a malfunction in the linear expansion valve. Ignoring this can lead to severe and irreparable damage to the compressor.

Additional Steps

Steps 1–2 are listed in Priority Fix.

1. 3

   Check the system for refrigerant leakage and correct the refrigerant amount to the proper level.

2. 4

   Inspect and test the linear expansion valve for proper operation. Refer to Section 10-6.

3. 5

   If all other components are confirmed functional, replace the outdoor controller board.