Indoor unit displays CH05 and does not respond, or outdoor unit does not start.

Safety: Turn off all power to both indoor and outdoor units at the breaker or disconnect before touching wiring.

Troubleshooting steps:

• Verify power: Ensure both indoor and outdoor units have proper supply voltage at their terminals according to the nameplate.
• Inspect communication cable: Locate the multi-core cable between indoor and outdoor units (often labeled 1-2-3 or L-N-C-S). Check for cuts, crushed sections, or signs of overheating.
• Check terminal wiring: Remove the covers at both indoor and outdoor connection blocks. Confirm that each terminal number/color matches exactly end-to-end. Tighten all terminal screws.
• Look for polarity issues: On many LG systems, the communication line must be correctly matched (e.g., terminal 3 to 3). Correct any miswiring.
• Test continuity: With power OFF, use a multimeter to check continuity of each conductor between indoor and outdoor. Repair or replace the cable if any conductor is open or shorted to another.
• Power reset: After correcting wiring, turn power back on and wait 5–10 minutes for the system to re-establish communication.

When to call a technician: If wiring and supply voltage are correct but CH05 remains, the indoor or outdoor PCB communication circuit may be defective and should be diagnosed with LG service tools.