Open/short of outdoor unit thermistors (TH3, TH32, TH33, TH6, TH7, and TH8)

What does U4 mean?

This fault indicates an open or short circuit detected in one or more of the outdoor unit thermistors (TH3, TH32, TH33, TH6, TH7, TH8) during compressor operation. Similar to U3, detection is inoperative for a period after compressor start and during defrosting for certain thermistors. This can lead to inaccurate system monitoring and control, potentially affecting performance and component longevity.

Additional Steps

Steps 1–2 are listed in Priority Fix.

1. 3

   Measure the resistance values of the affected thermistors and compare them to specifications, or check their temperature readings via microcomputer (refer to sections 10-6 and 10-10 for details).

2. 4

   If thermistors are functional and connections are secure, consider replacing the outdoor controller circuit board.