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U2

Mitsubishi Electric Split AC

Severity:

Source: OnlyErrorCodes.com — Every error code. One place.

Mitsubishi AC U2 Error — DC Overvoltage

What Does This Error Mean?

U2 on a Mitsubishi Electric AC means the inverter has detected DC bus overvoltage — voltage inside the inverter is too high for safe operation. The unit shuts down to protect the IGBT module and capacitors. Cause is usually mains supply spikes or inverter board fault.

Affected Models

  • Mitsubishi Electric MSZ-AP
  • Mitsubishi Electric MSZ-LN
  • Mitsubishi Electric MSZ-EF
  • Mitsubishi Electric MSZ-HR
  • Mitsubishi Electric MSZ-FH

Common Causes

  • Mains supply voltage spike from grid event or generator
  • Failed surge protection device upstream of the AC
  • Failed inverter board capacitor allowing voltage rise
  • Compressor regenerating energy back into the inverter
  • Faulty voltage sensor in the inverter (rare)

How to Fix It

  1. Power off the AC at the breaker.

    Switch off and leave for 30 minutes. Capacitors inside the inverter need time to discharge for the voltage protection to reset.

  2. Note any recent power events.

    U2 often appears the morning after a thunderstorm or grid event. Note the date for the technician — surge protection should be installed at the breaker panel after repair.

  3. Test mains voltage stability.

    Use a multimeter to check household voltage. Sustained high voltage (above 250V on a 230V system) causes recurring U2. If house voltage is high, contact the electricity provider.

  4. Check for nearby power-electronics interference.

    Solar inverters, EV chargers, or large motors on the same circuit can cause voltage transients that trigger U2. Move the AC to a different circuit if possible.

  5. Book Mitsubishi service.

    U2 typically needs inverter board inspection and possible capacitor replacement. Cost USD 350–700 fitted. Add a surge protector during the service to prevent recurrence — USD 50–100 extra.

When to Call a Professional

U2 is an inverter board fault that requires Mitsubishi-authorised service. Continued attempts to start risk damaging the IGBT module and capacitors — book service immediately.

Frequently Asked Questions

Will U2 damage my Mitsubishi AC?

U2 is a protection feature that prevents damage. However the underlying conditions (recurrent surges) can damage the board over time even with protection active. Address U2 by adding surge protection to the AC circuit.

Can a UPS prevent Mitsubishi U2?

A whole-circuit UPS (line-interactive type) protects against most spikes and sags. Cost USD 200–500 depending on AC capacity. Cheaper alternative: a DIN-rail surge protector at the breaker for USD 50–100. Both are much less than an inverter board replacement.