Indoor unit does not start; display shows A0 shortly after power-on

Safety first: Turn off the AC at the breaker and isolate power before removing covers. Use a non-contact voltage tester to confirm power is off.

• Check communication cable: Locate the 4‑core or 5‑core interconnecting cable between indoor and outdoor units. Inspect for cuts, rodent damage, or crushed insulation. If damaged, replace with the same gauge and type.
• Verify terminal connections: Remove the indoor front cover and access the terminal block. Tighten all screws for L, N, and communication terminals (often marked S, 1–2–3, or similar). Repeat at the outdoor unit terminal block.
• Match wiring order: Ensure the same terminal numbers and wire colors are matched indoor to outdoor. Incorrect order will trigger A0.
• Inspect PCBs: Look for burnt components, bulged capacitors, or darkened areas on both indoor and outdoor control boards. If visible damage is present, replace the affected PCB.
• Reset power: Restore power, wait 5 minutes, then restart the system to see if the code clears.

If A0 persists after cable and connection checks, a technician should test signal voltages and replace the faulty PCB.