Mitsubishi Electric U6 Error Code

What does Mitsubishi Electric U6 mean?

The control has detected a fault in the inverter power module that drives the compressor, so the compressor is stopped and U6 appears on a blinking display. The power module switches the high current to the compressor motor; an abnormality here can stem from the module itself, the compressor, or the supply, and it disables the outdoor unit to prevent damage.

Symptoms

• U6 shown on a blinking display
• Compressor will not start or stops on the protection device
• Unit trips shortly after attempting to run
• No cooling or heating output

Common causes

• Faulty inverter power module
• Compressor motor problem (winding fault or lock)
• Abnormal supply voltage to the outdoor unit
• Loose or damaged power wiring to the compressor

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Diagnostic steps

1. Power down fully

   Switch off the outdoor unit and wait before any restart attempt.

2. Check the supply

   Confirm the outdoor unit has correct, stable voltage on its power terminals.

3. Look for obvious damage

   Inspect for burnt smells, discoloration, or loose power connections in the electrical box.

4. Attempt one reset

   Restore power once and note whether U6 returns immediately or under load.

5. Stop further restarts

   If U6 persists, leave the unit off and arrange service to avoid further damage.

When to call a professional

U6 indicates a power-module fault and should be handled by a licensed technician. Testing the inverter module and compressor, and replacing the control board, involves high-voltage and refrigerant-side work. Repeated reset attempts can worsen the damage, so stop using the unit and have a qualified professional diagnose the power module and compressor.