The “Silent Treatment” Error
CH 05 is the most frequent error in LG Inverter ACs. It stands for Communication Error. Modern ACs use a dedicated wire (usually labeled ‘3’ or ‘C’) to send digital commands between the indoor unit (IDU) and outdoor unit (ODU).
The Logic: The Indoor PCB sends a “Ping”. If the Outdoor PCB doesn’t reply within a specific time window, the system assumes the connection is broken and triggers CH 05 to prevent uncoordinated operation.
1 DIY Checks (Try These First)
Total Power Reset
LG PCBs can get “stuck” due to voltage spikes. Switch off your main MCB. Wait 5 minutes. Turn it on. This resets the communication protocol.
Check Terminal Connections
Look at the wire block on the outdoor unit. Is the wire in slot ‘3’ (Communication) loose, rusted, or burnt? Carbon buildup here stops the signal.
Inspect for Rat Damage
The thick white cable connecting your indoor and outdoor units is a favorite snack for rats. Check visible sections for cuts or exposed copper.
Atlas Aircon Repair Protocol
How we fix the CH 05 Fault:
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01.
Continuity Test (The Loop) We short the wires at one end and test resistance at the other. If the multimeter doesn’t beep, the wire is broken inside the wall/insulation. We replace the cable.
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02.
PCB Signal Voltage Test We check the DC voltage between Terminal N and 3. It should fluctuate (pulse) between 0V and 70V DC. If it’s static, the PCB Comms circuit is dead.
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03.
Component Repair Often, the Optocoupler or Reactor on the Outdoor PCB fails. We can repair the PCB instead of replacing the whole board, saving you money.
Estimated Repair Cost (Atlas Aircon)