What It Means
Compressor stalled or seized with locked-rotor current levels detected.
Mitsubishi Electric All Systems
Mitsubishi Electric Error Code UF
Troubleshooting guide for the Mitsubishi Electric system fault UF.
Possible Causes
- Seized or mechanically locked compressor.
- Compressor winding short or ground fault.
- Excessive liquid refrigerant slugging causing hydraulic lock.
- Low supply voltage preventing compressor rotation.
- Failed or miswired inverter drive module.
Not sure which one it is — or if it's none of these? Try ACLogics today.
Disclaimer: This information is for general reference. Error codes can vary by model and production year. Always refer to your machine's specific manual and the information printed on the unit itself.
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Full Diagnosis
Error detail: the outdoor control board's current sensor detects the compressor drawing a locked-rotor level of current while running, indicating the compressor has stalled or seized rather than simply overloaded. The inverter/outdoor board cuts power to the compressor immediately to protect the windings and drive electronics, and the unit will not restart until the fault is manually cleared or enough retry cycles pass. This differs from U6, which trips on a sustained overload current while the compressor is still turning, and from UA, which is a terminal-relay-detected overcurrent rather than a current-sensor-detected locked-rotor condition.
All Recorded Causes
Seized or mechanically locked compressor. Failed compressor start/run capacitor or contactor. Compressor winding short or ground fault. Excessive liquid refrigerant flooding the compressor (slugging) causing hydraulic lock. Low supply voltage preventing the compressor from reaching running speed. Failed or miswired inverter/drive module. Blocked or restricted discharge line preventing rotation.
Verify Before Replacing Parts
- Confirm the exact Mitsubishi Electric model family and default context before acting on a generic code description.
- Confirm board LEDs, wiring polarity, and model compatibility before replacing control boards — this Mitsubishi Electric fault points at seized or mechanically locked compressor.
- Check for intermittent communication faults caused by connectors, moisture, or damaged harnesses, and rule out failed compressor start/run capacitor or contactor.
- After the correction, run the system long enough to confirm the default fault does not return under normal load.
Not sure which system this Mitsubishi Electric code is on?
ACLogics has guided diagnostics for 73 Mitsubishi Electric fault codes and asks the right questions to narrow it down.
