While the power is off, open the indoor unit’s electrical cover (be safe). Look at the TB5 terminal block. Are the communication wires (usually red/black or white/black) tightly screwed down? Loose wires cause constant communication resets. Do not skip this.
However, if you find yourself performing this reset weekly, stop. You have a systemic issue—likely noisy power, a failing outdoor main board (capacitor leak), or a water-damaged indoor communication harness. mitsubishi multi communication system reset
When in doubt, call a Mitsubishi Diamond Contractor. They have the MNET TOOL (PAC-USB-001) diagnostic software that can map the network and identify exactly which byte of data is corrupt. While the power is off, open the indoor
This is critical. The capacitors on the main PCB hold a charge for about 30-45 seconds. If you flip the breaker back on immediately, the RAM retains its corrupted state. Wait a full minute. Loose wires cause constant communication resets
When power returns, the outdoor unit will take 3 to 5 minutes to initialize. You will hear relays clicking and the fan might spin slowly. Do not touch the remote during this time. The indoor units are polling the outdoor for an address.
Do not just press the "Stop" button on the remote. Go to the electrical panel. Turn off the dedicated circuit breaker for the outdoor unit AND the indoor unit(s). You must kill power to the entire M-Net network.