Mitsubishi Air Conditioner Error Code E.OHT

The E.OHT error code on a Mitsubishi air conditioner indicates that an external thermal relay or a motor-internal thermal relay has been triggered and is currently in the ON state. Thermal relays are protective devices designed to interrupt control signals when a motor or connected component reaches a potentially damaging temperature threshold. When the inverter or control board detects that the OH (overheat) signal has been activated through one of the programmable input terminals, it logs this fault and halts operation to prevent motor winding damage or a broader system failure.

The OH signal is assigned through parameters Pr.178 to Pr.189, which map specific input terminals on the control board to their designated functions. If the OH function is not correctly assigned to the appropriate terminal, the unit may falsely trigger this error or fail to respond to a genuine overheat condition. Diagnosing this code requires confirming that the parameter assignment matches the physical wiring of the thermal relay, then checking whether the relay itself has actually tripped due to a real thermal event or has failed in the closed position.

Common causes of genuine thermal relay trips include restricted airflow around the motor, excessive ambient temperatures, prolonged operation under heavy load, or a failing motor with increased winding resistance that draws higher current and generates excess heat. A thermal relay that has tripped due to real overheating will typically reset automatically once temperatures return to a safe range, but recurrence indicates an underlying mechanical or electrical issue that must be resolved to prevent repeated faults.