Unit shows U3; compressor and fan do not start.

This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.

If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.

Possible Causes

Incorrect mode configuration, corrupted control logic, communication error between function modules, main PCB firmware issue

Safety: Turn off and unplug the unit.

Steps:

Factory reset (if supported): Consult the user manual for the specific Mitsubishi Electric model to perform a factory reset or initialization procedure.
Power cycle: Leave the unit unplugged for 15 minutes, then reconnect and test.
Check add‑on modules: If the unit has optional modules (e.g., Wi‑Fi, remote sensor), disconnect them and see if U3 clears.
Repair: Persistent U3 usually indicates a defective main control PCB that must be replaced.

Hard 4/5

Main Control PCB

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