Air Conditioner
LG
Updated Jul 17, 2026
LG AC CH21 Error — Inverter DC Overcurrent & How to Fix It
CH21
LG · Air ConditionerCH21 means the inverter circuit in the outdoor unit has detected excessive DC current. Thi…
Quick answer
CH21 means the inverter circuit in the outdoor unit has detected excessive DC current. This is a serious electrical fault — the compressor is drawing more current than the inverter can safely handle.
What CH21 means
The outdoor inverter board converts mains AC power to variable-frequency DC power for the compressor. CH21 triggers when the DC current exceeds the safe limit — either because the compressor is mechanically strained, the inverter power module (IPM) is failing, or there is a wiring fault.
This is one of the more serious LG error codes. The outdoor unit shuts down immediately to protect the inverter module from burning out.
This is a technician-level repair. CH21 involves high-voltage inverter circuits. Do not open the outdoor unit's electrical compartment unless you are a qualified HVAC electrician.
What to do
- Switch off at the breaker and do not restart for at least 30 minutes.
- Check the basics first: Is the outdoor coil very dirty? Is the fan running? Restricted airflow forces the compressor to work harder, which can trigger overcurrent.
- Clean the outdoor coil if dirty — hose it down gently.
- Restart once. If CH21 returns immediately, do not keep resetting — call a technician.
- Technician checks: The tech will measure compressor winding resistance, insulation resistance (megger test), check the IPM module, inspect the inverter PCB, and verify the incoming power supply.
What does the CH21 code mean?
CH21 indicates overcurrent in the outdoor inverter DC power circuit. The compressor is drawing more current than the inverter module can safely deliver.
Common causes
- Dirty outdoor condenser coil (compressor overworked)
- Failing compressor (winding short or mechanical seizure)
- Defective IPM (Intelligent Power Module) on the inverter PCB
- Wiring fault between inverter board and compressor
- Unstable or low incoming mains voltage
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How to fix the CH21 error
Switch off at the breaker
Do not restart for at least 30 minutes to let the inverter cool.
Clean the outdoor coil
Hose down the condenser to remove dirt blocking airflow.
Check the outdoor fan
Confirm it spins freely and starts when powered.
Restart once
If CH21 clears after cleaning, restricted airflow was the cause.
If CH21 returns, call a technician
The tech will megger-test the compressor, check the IPM, and inspect the inverter PCB.
Safety first: The outdoor inverter compartment carries lethal voltage even with the AC turned off (capacitor charge). Only a qualified technician should open it.
Part you may need: Inverter IPM module / compressor / outdoor inverter PCB
If the compressor windings are shorted to ground (low megger reading), the compressor needs replacing — the IPM alone will not fix it.
Frequently asked questions
Is CH21 expensive to fix?
It depends on the cause. A dirty coil is free. An IPM replacement is moderate. A dead compressor is expensive — get a warranty check first.
Can voltage problems cause CH21?
Yes — low or fluctuating mains voltage forces the inverter to draw more current. A voltage stabiliser helps prevent recurrence.
✎ Written by
REZAUL Karim (Riad)
REZAUL Karim (Riad) is the founder of ErrFixHub and a hands-on electronics and home-appliance repair specialist with over 15 years of experience diagnosing and fixing air conditioners, washing machines, refrigerators, inverters and other household appliances. He built ErrFixHub to turn cryptic error codes into clear, step-by-step fixes anyone can follow — cross-checking every code against manufacturer documentation and real repair-bench experience.
