Indoor unit stops and will not run; outdoor unit does not start; H11 displayed on indoor unit or remote.

Safety first: Turn off the air conditioner at the breaker and isolate power before removing covers. Risk of electric shock.

Steps to check:

• 1. Inspect interconnecting cable: Remove indoor and outdoor terminal covers. Verify the 3-core or 4-core interconnecting cable (often labeled 1-2-3 or 1-2-3-E) is firmly secured and not burnt, cut, or pinched. Tighten all terminal screws.
• 2. Confirm correct wiring order: Ensure the terminal numbers and wire colors match exactly between indoor and outdoor units. Mis-wiring can trigger H11.
• 3. Check for corrosion or water ingress: Look for rust or moisture on the outdoor terminal block and connectors. Dry and clean lightly with contact cleaner if minor; replace damaged terminals.
• 4. Inspect PCBs visually: With power still OFF, look at the indoor and outdoor control PCBs for burnt components, bulged capacitors, or blackened areas. If found, the PCB likely needs replacement.
• 5. Restore power and test: After tightening and confirming wiring, restore power and run the unit. If H11 persists, the communication circuit on either the indoor or outdoor PCB is likely faulty and should be tested/replaced by a qualified technician.

When to stop: If you are not comfortable working around live terminals or PCBs, do not proceed beyond visual inspection. Call a Panasonic-authorized service center.