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.

• Line voltage is either too high or too low for safe operation (U9 code).
• Synchronous signal loss or malfunction from the power grid.
• Power factor correction issue leading to voltage instability.
• Issues with the AC input power quality.

Click steps to track your progress.

1. 1

   Check the facility of the power supply.

2. 2

   Correct the U·V·W phase wiring to the compressor. Refer to section 10-9 (Outdoor power circuit board).

3. 3

   Replace the noise filter circuit board.

4. 4

   Check CN7C wiring.

5. 5

   Replace the ACT module.

6. 6

   Replace the outdoor power circuit board.