U9 (4220) - Power supply error (Undervoltage/Overvoltage/PAM/L1 open phase)

What does U9 mean?

The Mitsubishi Electric PUMY Air Conditioner system has detected an irregularity with the incoming power supply, such as voltage outside the normal range, a PAM error, or an open L1 phase. The system will stop operating.

• Unstable main power supply or voltage fluctuations
• Power outage or brownout condition
• Incorrect wiring or loose electrical connections
• Faulty power synchronization signal

Click steps to track your progress.

1. 1

   Note the error code displayed on the remote controller or outdoor unit.

2. 2

   Check if there are any widespread power issues or outages in your area.

3. 3

   Power off the Mitsubishi Electric PUMY Air Conditioner system at the main electrical breaker.

4. 4

   Wait for at least 30 seconds, then restore power to the system.

5. 5

   If the error persists, contact a qualified electrician or service technician to check the power supply and wiring connections.