LG Air Conditioner Error Code CH21

CH21 indicates a DC peak fault in the IPM section of the main control board. The current flowing through the IPM to the compressor exceeded the 32 to 38 ampere limit, so the system shut the compressor off to prevent damage. The root cause can be in the compressor itself, the PCB, or the refrigerant circuit.

No. The system has already shut the compressor off as a protective measure, so continued operation without resolving the fault risks permanent damage to the compressor or the IPM on the main board. Running the unit repeatedly through fault cycles can escalate a repairable issue into a full compressor or board failure.

Repair cost depends heavily on the root cause. Cleaning a blocked condenser or repairing wiring damage is relatively inexpensive, typically in the range of $75 to $200 for labor. Replacing the main PCB generally runs $300 to $600 including parts and labor. A compressor replacement is the most expensive outcome, often ranging from $700 to $1,500 or more depending on the unit size and labor rates in your area.

Some preliminary checks, such as cleaning a dirty condenser coil or inspecting wiring for visible damage, can be done by a knowledgeable DIYer. However, diagnosing IPM faults properly requires refrigerant gauges, a multimeter for winding resistance and insulation tests, and familiarity with high-voltage inverter circuits. Most repairs that follow this diagnosis, including compressor or PCB replacement, are best handled by a licensed HVAC technician.

A power cycle may temporarily clear the code and allow the unit to restart, but if the underlying cause is still present, the fault will return quickly, often within seconds of the compressor attempting to start. A reset is useful for confirming whether the fault is intermittent, but it is not a fix and should not be used as a substitute for diagnosis.