Mitsubishi Electric Mini-Split Code ED
Soft lockout
Serial communication error inside the outdoor unit. The outdoor controller board and the outdoor power board (or the M-NET board) cannot talk to each other.
Manual wording: “Serial communication error - Abnormal if serial communication between outdoor controller circuit board and outdoor power circuit board is defective.”
Documented for: PUZ-HA and other A-Control outdoor units with a separate power circuit board
Likely causes, most common first
- Breaking of wire or contact failure of connector CN2 between the outdoor controller board and the outdoor power circuit board
- Breaking of wire or contact failure of connector CN4 between the same two boards
- Defective communication circuit of the outdoor power circuit board
- Defective communication circuit of the outdoor controller circuit board
What you can safely check yourself
- Turn the system off at the breaker, wait one minute, and turn it back on once
When to call a technician
This is entirely internal to the outdoor unit's control boards. Call a technician.
A Mitsubishi Electric mini-split throwing this code repeatedly has a reason — clearing the code without fixing the cause just hides it.
Source
- Service Manual No. OCH750 Revised Edition-E - PUZ-HA Outdoor Units (May 2024) (Mitsubishi Electric, PUZ-HA24NHA1, PUZ-HA30NKA, PUZ-HA36NKA, PUZ-HA42NKA1 heat-pump outdoor units) · checked 2026-08-25