LG Air Conditioner Error Code 165

Error code 165 means the control system has detected an open or short circuit in the temperature sensor located on the rear-side heat exchanger (B) of the sub3 outdoor unit. This sensor is a thermistor that provides coil temperature data to the control board. When the board receives a signal outside the valid resistance range, it logs this code and may limit system operation. Diagnostics should follow the CH45 procedure specific to LG multi-outdoor unit systems.

A reset may temporarily clear the error from the display, but if the underlying sensor fault still exists the code will return as soon as the system attempts to read the sensor again. Resetting without repairing the sensor or wiring does not solve the problem and could allow the unit to operate outside safe parameters. The fault needs to be diagnosed and corrected before the error will stay cleared.

Repair costs depend on what component has failed. Replacing a thermistor sensor typically ranges from around 50 to 150 dollars including labor, while wiring harness repairs can vary widely based on the extent of damage. If the outdoor control board needs replacement, costs can range from 200 to 600 dollars or more depending on the model and labor rates in your area. A technician can provide an accurate estimate after completing the CH45 diagnostic procedure.

Basic checks such as inspecting the sensor connector for looseness or corrosion can be done by a knowledgeable DIYer with the unit powered down. However, accurately diagnosing a thermistor failure requires a multimeter and familiarity with reading NTC resistance values, and working inside a multi-outdoor unit involves high-voltage components. For most homeowners, calling a qualified HVAC technician is the safest approach.

Running the system with an active sensor fault is not recommended. The control board relies on this sensor to make decisions about compressor load and refrigerant flow in the outdoor unit. Without accurate temperature data, the system could overheat components or operate inefficiently, potentially causing additional damage. It is best to have the unit inspected before continuing extended operation.