Mitsubishi Air Conditioner Error Code MT3

MT3 is a maintenance signal output indicating that the inverter's cumulative energization time has reached or exceeded the threshold value set in parameter Pr.689. It is a scheduled service reminder, not a system fault or component failure. The unit uses this timer to prompt technicians to perform maintenance at defined operating hour intervals.

MT3 is a maintenance alert and not a critical fault, so the system typically continues to operate. However, continuing to run the unit without addressing the underlying maintenance need increases the risk of wear-related failures over time. It is recommended to schedule service promptly rather than ignoring the signal indefinitely.

The cost depends entirely on what type of maintenance the Pr.689 timer was set up to track. A basic inspection and filter service might cost between $75 and $200, while more involved work such as capacitor replacement, refrigerant service, or lubrication of mechanical components could range from $150 to $600 or more depending on the scope of service and local labor rates.

To clear MT3, first perform whatever maintenance activity the Pr.689 timer was configured to track, such as filter cleaning, refrigerant inspection, or component checks. After completing the required service, reset the cumulative energization timer in the inverter settings. If the Pr.689 value needs to be updated for the next interval, adjust it at that time before restarting the system.

Resetting the cumulative timer will clear the MT3 signal, but doing so without completing the associated maintenance defeats the purpose of the timer. The timer is there to protect the system by ensuring components are inspected or serviced at appropriate intervals. Always perform the required maintenance before resetting the counter.