Mitsubishi Electric Mini-Split 1 Blink
Soft lockoutShown as: Upper OPERATION INDICATOR lamp blinks steadily: 0.5 second ON, 0.5 second OFF, continuously
Miswiring or serial signal error. The indoor unit has not received the serial communication signal from the outdoor unit for 6 minutes, so the indoor and outdoor units are not talking to each other. Both units stop.
Manual wording: “Miswiring or serial signal - The serial signal from the outdoor unit is not received for 6 minutes.”
Documented for: MSZ-GL and MSY-GL indoor units (same pattern used across M-Series wall units)
Likely causes, most common first
- Indoor/outdoor connecting wire loose, disconnected or wired to the wrong terminals
- Power to the outdoor unit is off or its breaker is tripped
- Defective indoor or outdoor electronic control P.C. board
What you can safely check yourself
- Check that the breaker feeding the outdoor unit is on and has not tripped
- Turn the system off at the breaker, wait one minute, and turn it back on once
- Check that the outdoor unit is running and not iced over or blocked by snow or debris
When to call a technician
The connecting wire between the indoor and outdoor units carries line voltage and its polarity matters. Checking or correcting that wiring, and any board replacement, is a technician job.
A Mitsubishi Electric mini-split throwing this code repeatedly has a reason — clearing the code without fixing the cause just hides it.
Source
- Indoor Unit Service Manual No. OBH732 Revised Edition-D - MSZ-GL/MSY-GL Series (Mitsubishi Electric, MSZ-GL06NA/GL09NA/GL12NA/GL15NA/GL18NA/GL24NA and MSY-GL09NA/GL12NA/GL15NA/GL18NA/GL24NA wall-mounted indoor units) · checked 2026-08-25