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Error code reference

Mitsubishi Air Conditioner Error Code Er2

Write error during operation

Mitsubishi codesMitsubishi air conditioner codes

Write error during operation - parameter write attempted while Pr.77 = 0 and inverter is running.

First step from the service manual

Check that the inverter is stopped before writing parameters.

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

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What Er2 means on a Mitsubishi air conditioner

Er2 is a parameter write protection error that occurs on Mitsubishi inverter-driven air conditioning systems. It is triggered when a write operation is attempted on inverter parameters while the unit is actively running and the write protection parameter Pr.77 is set to 0. In this configuration, Pr.77 locks out parameter modifications during operation as a safeguard against unintended changes that could destabilize inverter performance or cause unsafe operating conditions.

The inverter control board manages motor speed, frequency output, and a range of operational parameters that govern compressor and fan behavior. When Pr.77 is set to 0, the system enforces a strict rule: parameters cannot be written while the inverter is in a running state. Any attempt to do so, whether from a connected programming device, a keypad, or an automated control sequence, will immediately generate the Er2 fault. The error is not caused by a hardware failure but by a procedural conflict between the write command and the current operational state of the inverter.

This error is most commonly encountered during commissioning, maintenance, or tuning sessions where a technician attempts to adjust parameters without first halting the inverter. It can also appear if a programmed controller or building management system sends parameter write commands at an incorrect point in the startup or shutdown sequence. Resolving Er2 does not require part replacement in most cases. The inverter must be fully stopped before any parameter write is attempted, or Pr.77 must be reconfigured to permit writes during operation if the application allows for it.

Source: manufacturer service documentation.

Common causes of Er2

  1. 01

    Parameter write attempted while inverter is running

    Wiring / connection

    The most frequent cause is a technician or control system attempting to write to inverter parameters without first stopping the unit. The system blocks this action when Pr.77 is set to 0.

  2. 02

    Pr.77 set to write-protect mode (value 0)

    Wiring / connection

    If Pr.77 is configured to 0, all parameter writes are blocked during operation by design. Reviewing and adjusting Pr.77 to an appropriate value may be necessary depending on the application requirements.

  3. 03

    Automated controller sending write commands at wrong time

    Wiring / connection

    A building management system, PLC, or other external controller may be programmed to send parameter write commands during an active run cycle. The timing logic in the controller sequence needs to be reviewed and corrected.

  4. 04

    Incorrect commissioning procedure followed

    Wiring / connection

    During initial setup or re-commissioning, parameters are sometimes adjusted in the wrong order or while the inverter has already started. Following the correct stop-then-write procedure eliminates this cause.

  5. 05

    Keypad or programming tool communication error

    Wiring / connection

    In rare cases, a faulty or incompatible programming keypad may send a write command unexpectedly during operation. Testing with a known-good programming device can confirm or rule this out.

See the test procedure for each cause

Frequently asked questions about Er2

What does Er2 mean on a Mitsubishi air_conditioner?
Er2 indicates a write error caused by an attempt to modify inverter parameters while the unit is running and Pr.77 is set to 0. This setting blocks parameter changes during active operation as a protection measure. The error is procedural, not a sign of hardware failure. Stopping the inverter before writing parameters will resolve the issue.
How do I fix Er2 on a Mitsubishi air conditioner?
Stop the inverter completely before attempting any parameter write operations. Once the unit is fully stopped, the write command can be executed without triggering Er2. If parameter writes during operation are required for your application, review the Pr.77 setting to determine whether it can be adjusted to permit writes while running.
Will resetting the unit clear the Er2 error?
A reset may clear the displayed error code, but Er2 will return immediately if the same parameter write is attempted again while the inverter is running. The underlying cause, a write command being sent during operation, must be corrected. Simply resetting without addressing the procedure or Pr.77 configuration will not provide a lasting fix.
Is Er2 a safety concern for my Mitsubishi air conditioner?
Er2 itself does not indicate a dangerous condition or component failure. It is a protective response that prevents the inverter from accepting potentially disruptive setting changes while it is actively running. The unit is functioning as designed when it generates this error. Address the write procedure and the unit will continue normal operation.
How much does it cost to repair an Er2 error on a Mitsubishi air conditioner?
Because Er2 is a configuration or procedural error rather than a parts failure, repair costs are typically limited to labor charges for a technician to diagnose and correct the parameter write sequence or Pr.77 setting. Expect service call fees in the range of 75 to 200 dollars depending on your location and the technician's time on site. No replacement parts are needed in most cases.

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