LG Air Conditioner Error Code 139

Error code 139 indicates that the excessive cooling outlet temperature sensor on the Sub2 outdoor unit in a 3-unit configuration has been detected as open or shorted. The control system cannot obtain a valid temperature reading from that sensor, so it triggers this fault code to protect the system. The fault must be diagnosed and repaired before the unit will resume normal operation.

Operating the system while error code 139 is active is not recommended. The Sub2 outdoor unit cannot properly monitor cooling outlet temperatures without a functioning sensor, which could allow the unit to run under abnormal thermal conditions and risk compressor damage. It is best to leave the system off until the sensor fault is resolved.

A power reset may temporarily clear the error from the display, but if the underlying sensor fault still exists, code 139 will return once the system restarts and the control board attempts to read the sensor again. A reset alone does not fix the open or short circuit condition in the sensor or its wiring. The physical fault must be identified and corrected for the error to clear permanently.

A knowledgeable DIYer can start by checking the sensor connector on the Sub2 outdoor unit for looseness, corrosion, or visible wiring damage and reseating or cleaning it. Measuring the sensor resistance with a multimeter is also within reach if you have basic electrical skills. However, replacing the sensor or control board, and working inside a multi-unit outdoor system, is generally best handled by a certified HVAC technician due to the complexity of the refrigerant and electrical systems involved.

Repair costs vary depending on the root cause. If only a connector needs cleaning or reseating, the cost may be limited to a service call fee, typically in the range of $75 to $150. A replacement temperature sensor generally adds $20 to $80 in parts. If the wiring harness or control board requires replacement, total repair costs can range from $200 to $600 or more depending on labor rates and parts availability.