LG HVAC Error Code 42

Error code 42 on an LG HVAC system means the low pressure switch has opened because the refrigerant pressure on the suction side of the system dropped below 14 PSI. This is a protective shutdown designed to prevent compressor damage. The system will not operate until the underlying pressure issue is resolved and the fault is cleared.

The error itself is a safety feature, not a hazard indicator. The system is protecting the compressor from running under dangerously low pressure. However, if the fault is caused by a refrigerant leak, prolonged exposure to certain refrigerants in an enclosed space can be a health concern. Address the fault promptly and ensure adequate ventilation if you suspect a refrigerant leak indoors.

Repair costs depend heavily on the cause. Replacing an air filter is a low-cost fix typically in the range of $10 to $30 for parts. If the system requires refrigerant leak detection, repair, and recharging, costs can range from $200 to $600 or more depending on the leak location and refrigerant type. A faulty expansion valve replacement can range from $150 to $400 including labor. A service diagnostic visit alone typically costs $75 to $150.

Some basic checks are accessible to a knowledgeable homeowner, such as inspecting and replacing a clogged air filter or verifying that outdoor temperatures are within the system's operating range. However, if the cause involves refrigerant loss or a faulty expansion valve, a licensed HVAC technician is required to handle refrigerants and perform pressure testing. Attempting to add refrigerant without identifying and repairing a leak will not solve the problem.

Resetting the unit may temporarily clear the fault code and allow the system to restart, but the error will return if the root cause has not been corrected. If suction pressure remains below 14 PSI, the low pressure switch will open again and shut the system down. A reset should only be performed after diagnosing and addressing the underlying issue.