Overvoltage/Undervoltage & Synchronous Signal Issue

What does U9 (0) mean?

This fault is detected during compressor operation if the DC bus voltage decreases to 310V, momentarily drops to 300V, or increases to 700V. It can also be triggered if the outdoor unit input current drops to 0.4A when operating frequency is >=30Hz or compressor current is >=3A. Root causes may include unstable power supply, compressor wiring issues, a defective noise filter circuit board, a faulty ACT module, its drive circuit, or loose connections for CN7C, CNAF, CN50, or CN51.

Additional Steps

Steps 1–2 are listed in Priority Fix.

1. 3

   Replace the noise filter circuit board.

2. 4

   Check CN7C wiring.

3. 5

   Replace the ACT module.

4. 6

   Replace the outdoor power circuit board.