LG Air Conditioner Error Code 120

Error code 120 means the compressor suction pipe temperature sensor on the sub1 outdoor unit is detecting an open or short circuit condition. The control board cannot get a valid temperature reading from this thermistor, so the system shuts down to protect the compressor. Diagnosis should follow the CH46 troubleshooting procedure, which covers sensor resistance checks and wiring inspection.

No, you should not attempt to bypass or continue operating the system while this error is active. The suction pipe temperature sensor is part of the compressor protection system. Running the unit without a valid sensor reading could allow the compressor to operate under unsafe conditions, potentially causing compressor damage or complete failure.

Repair costs vary depending on the specific fault found. If only the suction pipe thermistor needs replacement, parts and labor typically range from around $75 to $200. If the outdoor control board has failed, costs can range from $200 to $600 or more depending on the model and labor rates in your area. A service call for diagnosis alone generally runs $75 to $150 before any parts.

Some basic checks, such as inspecting visible wiring and connectors for obvious damage or disconnection, can be done by a knowledgeable homeowner. However, accurately diagnosing an open or short in a thermistor requires a multimeter and familiarity with the outdoor unit wiring layout. Replacing components inside the outdoor unit, particularly on multi-unit systems, is best handled by a qualified HVAC technician.

A power reset may temporarily clear the error and allow the unit to restart, but if the underlying sensor or wiring fault still exists, the code will return quickly. The root cause must be diagnosed and repaired before the error will clear permanently. Repeated resets without repair can risk compressor damage.