The “DC Peak” Electrical Crash
The CH 21 Error is one of the most serious faults in LG Inverter ACs. It refers to the IPM (Intelligent Power Module), the large black chip under the aluminum heat sink on the outdoor PCB.
Why it happens: This chip converts DC power to AC to drive the compressor. If there is a sudden voltage surge, or if the compressor windings are shorted, the IPM tries to draw infinite current (DC Peak). To prevent an explosion, it trips instantly.
1 Technician-Level Checks (Dangerous Voltage)
Check Heat Sink Paste
The IPM generates massive heat. If the white thermal paste under the aluminum heatsink has dried up, the IPM overheats and triggers CH 21.
Compressor “Megger” Test
Disconnect the compressor wires. Check resistance between the terminals and the copper pipe. If there is continuity, the compressor is Grounded and killing the PCB.
Voltage Surge History
Did the error appear after a thunderstorm or power cut? 80% of CH 21 errors are caused by grid fluctuations blowing the IPM.
Atlas Aircon Repair Protocol
We fix the board, saving you the cost of a new AC:
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01.
Component Level Repair Instead of replacing the whole expensive PCB (₹8,000+), we desolder the blown IPM chip and replace it with a genuine LG spare part.
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02.
Heat Sink Re-Pasting We clean the old dried paste and apply high-grade thermal compound to ensure the new IPM stays cool even at 45°C ambient temp.
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03.
Compressor Protection Check We test the U-V-W balance of the compressor windings to ensure it won’t just blow the new PCB again immediately.
Estimated Repair Cost (Atlas Aircon)