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Error code reference

Mitsubishi Air Conditioner Error Code E.THM

Motor overload trip

Mitsubishi codesMitsubishi air conditioner codes

Motor overload trip - electronic thermal O/L relay detected motor overheat caused by overload or reduced cooling during low-speed operation.

First step from the service manual

Check the motor for use under overload and verify Pr.71 Applied motor setting is correct.

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

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What E.THM means on a Mitsubishi air conditioner

The E.THM error code on a Mitsubishi air conditioner indicates an electronic thermal overload relay trip, meaning the drive's built-in motor protection circuit has detected that the motor is operating under conditions that produce excessive heat. The electronic thermal overload relay (O/L relay) continuously monitors motor current and thermal accumulation. When the calculated thermal load exceeds the programmed threshold, the drive trips and generates E.THM to prevent motor winding damage. This protection mimics the behavior of a physical thermal relay but uses current sensing and software modeling to estimate motor temperature.

The two primary triggers for this fault are true motor overload and insufficient cooling during low-speed operation. Under overload conditions, the motor draws more current than its rated capacity, generating heat faster than it can dissipate. During low-speed operation, the motor's built-in cooling fan runs slower, reducing airflow across the windings, which means even rated current can produce dangerous thermal accumulation. The parameter Pr.71, which defines the applied motor type and its thermal characteristics, must be configured correctly for the thermal model to calculate protection thresholds accurately. An incorrect Pr.71 setting can cause nuisance trips or, more dangerously, allow real overheating to go undetected.

Diagnosis should begin by confirming that the mechanical load on the motor is within its rated specifications and that no mechanical binding or excessive resistance is present in the driven system. After ruling out a true overload condition, verify that Pr.71 is set to match the actual motor connected to the drive. Also inspect the motor's cooling pathway, particularly in variable-speed applications where extended low-speed operation is common.

Source: manufacturer service documentation.

Common causes of E.THM

  1. 01

    True motor overload condition

    Wiring / connection

    The motor is driving a mechanical load that exceeds its rated capacity, causing it to draw excessive current and overheat. Check for mechanical binding, seized bearings, or an improperly sized load connected to the motor.

  2. 02

    Incorrect Pr.71 Applied Motor setting

    Wiring / connection

    If Pr.71 is not set to match the actual motor type in use, the electronic thermal relay's protection model uses incorrect thermal characteristics, leading to nuisance trips. Verify the parameter value matches the motor specification.

  3. 03

    Insufficient motor cooling during low-speed operation

    Wiring / connection

    At reduced speeds, the motor's integral cooling fan moves less air across the windings, reducing heat dissipation. Extended low-speed operation without adequate external cooling can accumulate enough thermal load to trigger E.THM even at normal current levels.

  4. 04

    Worn or failing motor windings

    Part replacement

    Degraded winding insulation or shorted turns increase resistive losses and heat generation within the motor. A winding resistance check and insulation resistance test can reveal this condition.

  5. 05

    Blocked or restricted airflow around the motor

    Wiring / connection

    Dust buildup, debris, or a failed cooling fan can restrict airflow around the motor housing, reducing its ability to shed heat. Inspect the motor exterior and any ventilation paths for obstructions.

See the test procedure for each cause

Frequently asked questions about E.THM

What does E.THM mean on a Mitsubishi air_conditioner?
E.THM indicates that the electronic thermal overload relay within the drive has tripped due to detected motor overheat. The protection circuit determined that the motor was operating under overload conditions or was not receiving sufficient cooling while running at low speed. The system shuts down automatically to protect the motor from winding damage. A technician should check the mechanical load on the motor and confirm the Pr.71 parameter is set correctly for the installed motor.
Can I reset the E.THM error myself, and will that fix the problem?
You can reset the fault after the motor has cooled down, but resetting alone will not fix the underlying cause. If the overload condition or cooling issue is not corrected, the fault will return, often in a shorter time as thermal accumulation restarts. Resetting without diagnosis risks repeated trips and eventual motor damage.
Is it safe to keep using the air conditioner with an E.THM error showing?
No, you should not continue operating the unit while this fault is active. The E.THM error indicates the motor protection circuit has already tripped the system to prevent overheating. Bypassing or repeatedly resetting the fault without addressing the root cause can lead to permanent motor winding failure and create a potential fire or electrical safety hazard.
How much does it cost to repair an E.THM fault on a Mitsubishi air conditioner?
Repair cost depends heavily on the root cause. If the fix involves correcting a parameter setting like Pr.71, the cost may be limited to a service call fee, typically in the range of $75 to $200. If the motor requires replacement, parts and labor combined can range from $300 to $900 or more depending on the motor size and unit model.
What is the Pr.71 parameter and why does it matter for this fault?
Pr.71 is the Applied Motor setting in the drive's parameter configuration. It tells the drive what type of motor is connected, which directly affects how the electronic thermal overload relay calculates the motor's thermal model and protection thresholds. If Pr.71 is set incorrectly, the thermal protection curve will not match the actual motor, causing either premature E.THM trips or insufficient protection against real overheating.

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