Mitsubishi Electric · R410A Systems
There is an error in the physical or communication connection between the indoor and outdoor units. This prevents proper system operation, as commands and status updates cannot be exchanged.
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Inspect the communication wiring terminals on both indoor and outdoor unit PCBs for secure connections and proper seating.
Check for correct polarity of communication wiring (e.g., A/B or +/- terminals, as applicable).
Verify that the total communication line length does not exceed specified installation limits.