Mitsubishi Air Conditioner Error Code E.THT

E.THT indicates that the inverter's output transistor elements exceeded their allowable temperature while the unit was operating at or above rated current output. The inverter protection system trips the unit when the load exceeds 150% of rated current for more than 60 seconds. This is a thermal protection fault designed to prevent permanent damage to the inverter's power transistor components.

No, you should not continue operating the unit after an E.THT fault. The error means the inverter has already reached a dangerous thermal threshold and has shut down to protect itself. Repeatedly forcing the system to restart without addressing the underlying cause can result in permanent damage to the output transistors or other inverter components.

Repair costs vary widely depending on the cause. A parameter adjustment by a technician may cost relatively little, typically in the range of a standard service call fee. Replacing a failed inverter cooling fan or related components can range from moderate to higher costs depending on parts and labor. If the inverter module or IGBT elements need replacement, costs can be significantly higher, potentially ranging from several hundred to over a thousand dollars depending on the unit model and component pricing.

Some causes of E.THT, such as incorrect acceleration, deceleration, or torque boost parameter settings, can be corrected by a knowledgeable technician or experienced DIYer with access to the inverter configuration interface. However, causes involving compressor current draw, IGBT condition, or inverter cooling components require electrical testing and component inspection that is best handled by a qualified technician. Working inside an inverter-driven air conditioner involves high-voltage DC bus circuits that are dangerous without proper training and equipment.

A reset may clear the fault temporarily and allow the unit to restart, but the error will return if the root cause is not corrected. If the fault is due to a parameter setting issue, correcting the setting before resetting will produce a lasting fix. If the cause is mechanical or component-related, such as a stressed compressor or degraded IGBTs, the fault will recur under similar operating conditions.