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Error code reference

Mitsubishi Air Conditioner Error Code E.THT

Inverter overload trip

Mitsubishi codesMitsubishi air conditioner codes

Inverter overload trip - output transistor element temperature exceeded protection level while current flows at rated output current level or higher (permissible overload 150% 60s).

First step from the service manual

Check that acceleration/deceleration time is not too short and torque boost setting is appropriate.

The complete diagnostic procedure includes additional test steps, resistance specifications, wiring diagram references, and component test points.

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What E.THT means on a Mitsubishi air conditioner

The E.THT error code on a Mitsubishi air conditioner indicates an inverter overload trip caused by the output transistor element temperature exceeding its protection threshold. This condition occurs specifically while current is flowing at or above the rated output current level. The inverter's built-in protection logic monitors the thermal state of the output transistor elements (IGBTs) and trips the system when the permissible overload limit of 150% for 60 seconds is exceeded. This is a thermal and electrical protection mechanism designed to prevent permanent damage to the power transistor components within the inverter drive circuit.

The root cause is typically excessive mechanical or electrical load on the compressor motor combined with inverter drive parameters that push the output transistors beyond their safe operating temperature. When the acceleration or deceleration ramp times are set too short, the inverter demands high current output in a compressed timeframe, generating rapid heat buildup in the transistor elements. Similarly, an incorrectly configured torque boost setting can force the inverter to supply excessive current at low frequencies, compounding the thermal stress on the output stage.

Diagnosing this fault begins with reviewing the inverter parameter settings for acceleration and deceleration times and confirming the torque boost is calibrated appropriately for the connected load. Beyond parameter issues, restricted airflow around the inverter module, a failing inverter cooling fan, or a compressor that is mechanically stressed or drawing abnormally high current can all contribute to repeated E.THT trips. Ambient temperature conditions in the equipment space should also be evaluated, as high ambient temperatures reduce the inverter's thermal headroom.

Source: manufacturer service documentation.

Common causes of E.THT

  1. 01

    Acceleration or deceleration time set too short

    Wiring / connection

    If the inverter ramp times are configured too aggressively, the output transistors must deliver very high current in a short period, generating excessive heat. Review and extend the acceleration and deceleration time parameters in the inverter settings.

  2. 02

    Incorrect torque boost setting

    Wiring / connection

    An overly high torque boost forces the inverter to supply excess current at low operating frequencies, increasing transistor temperature beyond safe limits. Verify the torque boost parameter matches the load requirements of the compressor.

  3. 03

    Compressor drawing excessive current

    Part replacement

    A mechanically stressed or failing compressor can draw current at or above 150% of the rated level, triggering the overload protection. Measure compressor operating current and compare it to the rated value to identify abnormal draw.

  4. 04

    Inadequate cooling of the inverter module

    Part replacement

    Blocked airflow, a failed inverter cooling fan, or high ambient temperatures in the equipment enclosure reduce the inverter's ability to dissipate heat, causing transistor temperatures to rise faster under load. Inspect the inverter heatsink, cooling fan operation, and installation environment.

  5. 05

    Degraded or failing output transistor (IGBT) elements

    Part replacement

    Worn or partially damaged IGBTs within the inverter output stage have reduced thermal efficiency and will overheat sooner under normal operating loads. This is typically identified after confirming all parameters and mechanical conditions are correct but the fault persists.

See the test procedure for each cause

Frequently asked questions about E.THT

What does E.THT mean on a Mitsubishi air_conditioner?
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.
Can I fix E.THT myself, or do I need a technician?
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.
Is it safe to keep running my air conditioner when E.THT appears?
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.
Will resetting the unit clear the E.THT error?
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.
How much does it cost to repair an E.THT error on a Mitsubishi air conditioner?
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.

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