Mitsubishi Air Conditioner Error Code TH

The TH error code on a Mitsubishi air conditioner indicates that the electronic thermal relay function has entered a pre-alarm state. Specifically, the cumulative thermal value calculated by the inverter drive has reached or exceeded 85% of the threshold set in parameter Pr.9. The electronic thermal relay is a software-based protective function that simulates the behavior of a physical thermal overload relay by tracking the motor's heat accumulation over time. It continuously monitors current draw relative to the motor's rated capacity and integrates that data into a running thermal value. Once that value crosses the 85% mark of the Pr.9 setting, the TH code is triggered as a warning before full trip shutdown occurs.

This pre-alarm is intended to give technicians and control systems an opportunity to intervene before the unit hits the full overcurrent thermal trip limit. The most common scenarios that drive the thermal accumulation value this high include sustained heavy loads, frequent start-stop cycling, and sudden acceleration events that spike current draw beyond the motor's rated operating range. If Pr.9 is configured incorrectly for the specific motor or compressor being driven, the threshold may be set too low relative to normal operating current, causing nuisance pre-alarms even under acceptable load conditions.

Diagnosing TH requires evaluating both the operating conditions and the parameter configuration. The first step is to check whether the unit has been subjected to abnormally high or sustained loads, or whether recent changes to system conditions have introduced sudden acceleration demands. If operating conditions appear normal, reviewing and adjusting the Pr.9 setting to match the actual motor nameplate rating is essential. The pre-alarm does not immediately shut down the system, but if the root cause is not addressed, the thermal value will continue climbing toward a full fault trip.