LG Air Conditioner Error Code E311

E311 indicates an error with the liquid pipe temperature sensor on the sub heat exchanger. The control board has detected either a short circuit or an open circuit condition from this thermistor. This prevents the system from accurately monitoring refrigerant temperature at that point in the circuit, causing the unit to shut down or restrict operation.

Operating the unit while E311 is active is not recommended. Without accurate liquid pipe temperature data, the system cannot properly control refrigerant flow, which can lead to inefficient operation or potential damage to compressor and refrigerant circuit components. The unit should be diagnosed and repaired before returning it to regular use.

If only the sensor connector needs to be reseated, there may be no parts cost and a minimal service call fee. If the thermistor itself needs replacement, parts typically range from $15 to $60 depending on the model, with labor costs varying by region and service provider. If the control PCB is at fault, board replacement can range from $150 to $400 or more, making a thorough diagnostic important before ordering components.

The first step, checking that the sensor connector is firmly seated on the PCB, is something a knowledgeable DIYer can perform safely with the unit powered off. If the connector is secure, measuring thermistor resistance requires a multimeter and some familiarity with reading resistance values. Replacing the thermistor or wiring harness involves working inside the unit and, in some configurations, near refrigerant components, so professional service is recommended if basic connector checks do not resolve the fault.

A power reset may temporarily clear the displayed error code, but if the underlying sensor or wiring fault still exists, the E311 code will return once the system runs through its self-diagnostic checks. A reset alone is not a repair. The sensor connector, wiring, and thermistor resistance must be inspected and corrected to permanently resolve the fault.