LG Air Conditioner Error Code CH42

CH42 on an LG air conditioner indicates that the low pressure sensor circuit has been detected as either open or shorted. The low pressure sensor monitors refrigerant pressure on the suction side of the system and sends a continuous signal to the control board. When that signal is absent or abnormal, the unit stops operating and displays CH42 to alert the technician to a sensor or wiring fault.

No. The unit will typically shut itself down when CH42 is active, and you should not attempt to bypass this shutdown. The low pressure sensor protects the compressor from running under low refrigerant conditions. Operating without this protection risks serious compressor damage, which is far more expensive to repair than the sensor or wiring fault itself.

A power reset may temporarily clear the error code display, but if the underlying sensor or wiring fault is still present the code will return as soon as the unit attempts to operate. Resetting the unit without repairing the fault does not fix the problem and continues to leave the compressor without low pressure protection. The physical fault in the sensor circuit must be corrected for the error to clear permanently.

A knowledgeable DIYer can check for obvious issues such as loose connectors or visibly damaged wiring, but diagnosing and replacing a low pressure sensor involves working near the refrigerant circuit and interpreting electrical test results. Because this fault disables a compressor protection system, having a qualified HVAC technician complete the diagnosis and repair is strongly recommended.

Repair costs depend on the root cause. If only a loose connector is involved, the labor cost for a service call may be the primary expense, typically in the range of $75 to $150. Replacing the low pressure sensor itself generally costs between $150 and $350 including parts and labor. If the control board has failed, costs can range from $300 to $600 or more depending on the unit model.