mypros+
Error code reference

Mitsubishi Air Conditioner Error Code MT3

Maintenance signal output 3

Mitsubishi codesMitsubishi air conditioner codes

Maintenance signal output 3 - inverter cumulative energization time reached or exceeded Pr.689 set value.

First step from the service manual

Take appropriate countermeasures according to the purpose of maintenance timer setting.

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

MyPros+ Max

Get the full diagnostic procedure for MT3.

  • Step-by-step tests with expected resistance, voltage, and continuity values
  • Wiring diagram references and connector pinouts from the OEM service manual
  • Verified part numbers when replacement is required
Get the full procedure

$29/month · Cancel anytime · Or $9.95 3-day pass

What MT3 means on a Mitsubishi air conditioner

The MT3 error code on a Mitsubishi air conditioner is a maintenance signal output, not a system fault. It triggers when the inverter's cumulative energization time meets or exceeds the threshold value configured in parameter Pr.689. This parameter allows technicians or facility managers to set a specific runtime interval, measured in hours, after which the unit signals that scheduled maintenance is due. The MT3 signal is the third of the available maintenance timer outputs and is designed to prompt inspection or servicing of components whose wear is tied directly to operating hours.

The inverter tracks total energization time continuously and compares it against the Pr.689 set value. Once that threshold is reached or exceeded, the MT3 output is triggered. This is a programmed alert rather than an indication that any component has actually failed. The system continues to operate normally in most configurations, but the signal is intended to prompt action before a failure occurs. Common maintenance activities tied to this timer include filter cleaning, refrigerant checks, lubrication of moving parts, or inspection of electrical contacts and capacitors.

Addressing MT3 requires taking countermeasures appropriate to whatever purpose the Pr.689 timer was originally configured for. Once the required maintenance has been performed, the cumulative timer should be reset and the Pr.689 value reviewed or updated as needed. Ignoring the MT3 signal and simply resetting the counter without performing the associated maintenance defeats the purpose of the timer and may lead to premature component failure or reduced system efficiency over time.

Source: manufacturer service documentation.

Common causes of MT3

  1. 01

    Scheduled maintenance interval reached

    Wiring / connection

    The most common reason for MT3 is straightforward: the inverter has accumulated enough operating hours to reach the threshold set in Pr.689. This is the intended function of the code and means a scheduled maintenance visit is due.

  2. 02

    Pr.689 parameter set too low

    Wiring / connection

    If MT3 appears sooner than expected, the Pr.689 value may have been configured for a shorter interval than intended. Review the parameter setting and adjust it to the appropriate maintenance interval for the installation.

  3. 03

    Cumulative timer not reset after last service

    Wiring / connection

    If maintenance was recently performed but the energization timer was not reset afterward, MT3 will trigger again immediately or very quickly. Resetting the cumulative counter after each service visit is a required step.

  4. 04

    Worn or dirty components triggering early inspection need

    Part replacement

    In some installations, MT3 is configured to align with specific component service intervals such as filter replacement, capacitor inspection, or belt and bearing checks. If the unit has been operating in a demanding environment, those components may need attention at or before the triggered interval.

  5. 05

    Parameter configuration not documented at site

    Wiring / connection

    If the purpose of the Pr.689 setting is unknown to the current service technician, the maintenance intent behind MT3 cannot be properly fulfilled. Reviewing original commissioning documentation or querying the control system parameters is necessary before resetting.

See the test procedure for each cause

Frequently asked questions about MT3

What does MT3 mean on a Mitsubishi air_conditioner?
MT3 is a maintenance signal output indicating that the inverter's cumulative energization time has reached or exceeded the threshold value set in parameter Pr.689. It is a scheduled service reminder, not a system fault or component failure. The unit uses this timer to prompt technicians to perform maintenance at defined operating hour intervals.
How do I fix or clear the MT3 code on a Mitsubishi air conditioner?
To clear MT3, first perform whatever maintenance activity the Pr.689 timer was configured to track, such as filter cleaning, refrigerant inspection, or component checks. After completing the required service, reset the cumulative energization timer in the inverter settings. If the Pr.689 value needs to be updated for the next interval, adjust it at that time before restarting the system.
Is it safe to keep running my Mitsubishi air conditioner while MT3 is showing?
MT3 is a maintenance alert and not a critical fault, so the system typically continues to operate. However, continuing to run the unit without addressing the underlying maintenance need increases the risk of wear-related failures over time. It is recommended to schedule service promptly rather than ignoring the signal indefinitely.
Will simply resetting the MT3 code fix the problem?
Resetting the cumulative timer will clear the MT3 signal, but doing so without completing the associated maintenance defeats the purpose of the timer. The timer is there to protect the system by ensuring components are inspected or serviced at appropriate intervals. Always perform the required maintenance before resetting the counter.
How much does it cost to address an MT3 maintenance alert on a Mitsubishi air conditioner?
The cost depends entirely on what type of maintenance the Pr.689 timer was set up to track. A basic inspection and filter service might cost between $75 and $200, while more involved work such as capacitor replacement, refrigerant service, or lubrication of mechanical components could range from $150 to $600 or more depending on the scope of service and local labor rates.

Related Mitsubishi air conditioner codes

All Mitsubishi air conditioner codes
View all 79 Mitsubishi air conditioner codes

78,000+ service manuals · 160,000+ error codes · 55+ brands

Get Started

$29/month · Cancel anytime · Or $9.95 3-day pass