EC

Indoor/Outdoor Unit Miswiring or Excessive Indoor Units

Mitsubishi Electric · PAR-21MAA MA Remote Controller

What does EC mean?

This communication error is detected when there is incorrect wiring of the indoor/outdoor connecting wire or if more than four indoor units are connected to the outdoor unit. This prevents proper communication and control between the indoor and outdoor units, leading to system malfunction.

Repair Steps

  1. 1

    Verify the indoor/outdoor connecting wire terminations match the wiring diagram for correct connection.

  2. 2

    Count the number of connected indoor units and confirm it does not exceed the maximum allowed limit of four units for this outdoor unit.

  3. 3

    Inspect the indoor/outdoor connecting wire and power supply for signs of electrical noise interference.

  4. 4

    Cycle power to the unit (turn off, then on again) to re-check for the error.

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Verified technical data. Last updated: March 2026
Source: Mitsubishi Electric PAR-21MAA MA Remote Controller