LG Air Conditioner Error Code 127

Error code 127 on an LG air conditioner indicates that the Sub1 outdoor unit's excessive cooling outlet temperature sensor has been detected as either open or shorted. The control board cannot receive a valid temperature reading from this sensor and has flagged the fault to protect the system. This is a sensor circuit fault specific to the sub outdoor unit in a multi-unit or multi-module outdoor configuration.

It is not recommended to continue running the system with this error active. The outdoor unit control board relies on this sensor to monitor refrigerant temperatures at the cooling outlet, and operating without valid sensor data could allow the system to run outside safe thermal limits. The unit may restrict operation or shut down automatically as a protective measure.

A power reset may temporarily clear the error code from the display, but if the underlying sensor fault still exists, the code will return once the unit attempts to operate and reads the sensor again. Resetting is useful for confirming whether the fault is intermittent, such as from a loose connector, but a permanent fix requires identifying and correcting the open or short circuit in the sensor wiring or replacing the sensor itself.

Some steps are accessible to a knowledgeable DIYer, such as inspecting the sensor connector for looseness, visible wire damage, or corrosion. Measuring sensor resistance with a multimeter is also a straightforward test. However, accessing the outdoor unit control board and replacing refrigerant-side components typically requires an HVAC technician, especially if refrigerant handling is involved.

If only the temperature sensor needs replacement, parts typically range from $15 to $60 depending on the sensor type, with labor adding $75 to $200 depending on your region and service provider. If the control board is at fault, board replacement costs can range from $150 to $500 or more for parts alone. A technician diagnostic visit is usually required to confirm which component has failed before parts are ordered.