4220 <4320> (U9) Undervoltage/overvoltage/PAM error/L1 open phase/power synchronization signal error

What does 4220 <4320> (U9) mean?

This is a broad power supply error indicating voltage fluctuations (too low or too high), an open phase, or a problem with the power synchronization signal. It can stem from issues with the main power supply or internal electrical components.

• Decrease or increase of power supply voltage.
• L1 open-phase (Y model only).
• Primary current sensor failure.
• Disconnection of compressor wiring.
• Malfunction of 52C relay.
• Defective outdoor power circuit board.

Click steps to track your progress.

1. 1

   Check the main power supply to the outdoor unit to ensure it is stable and within acceptable voltage ranges.

2. 2

   Verify that all compressor wiring connections are secure and undamaged.

3. 3

   Turn off the power to the outdoor unit at the main breaker for 5-10 minutes, then restore power to reset the system.

4. 4

   If possible, check for an open phase condition (L1) if you have a 'Y model' unit (this typically requires a multimeter and a qualified electrician).

5. 5

   If the error persists, contact a qualified electrician or HVAC technician to inspect the outdoor power circuit board and relays.