LG Air Conditioner Error Code 45

Error code 45 on an LG air conditioner indicates a fault with the outdoor unit heat exchanger temperature sensor on the front side of the coil. The system has detected either an open circuit or a short circuit in that sensor, meaning the resistance reading is outside the valid operating range. The unit shuts down to prevent potential damage from unmonitored heat exchanger temperatures. Diagnosis involves checking the sensor connector at the PCB and measuring sensor resistance with a multimeter.

No, you should not attempt to operate the unit while error code 45 is active. The outdoor heat exchanger temperature sensor is a critical safety and control input, and the system has shut down specifically because it cannot verify safe operating temperatures. Running the unit without valid sensor feedback could lead to compressor overheating or other component damage.

Resetting the unit by cycling power may temporarily clear the error code display, but the fault will return as soon as the system restarts and the PCB reads the sensor again. Because error code 45 is triggered by a measurable electrical fault, such as an open or shorted sensor circuit, it will not resolve on its own without addressing the underlying cause. A reset is only useful as a step to confirm the fault is repeatable, not as a repair solution.

A knowledgeable DIYer can check whether the sensor connector is fully seated on the outdoor PCB, which requires only basic access to the outdoor unit. Testing sensor resistance with a multimeter is also within reach for someone comfortable with basic electrical diagnostics. However, if the sensor or PCB needs replacement, working inside the outdoor unit involves components near high-voltage circuits, so professional service is strongly recommended for those without electrical repair experience.

If the fix is simply reseating a loose connector, there may be no parts cost, though a service call diagnostic fee typically ranges from $75 to $150. Replacing the heat exchanger thermistor sensor is generally an affordable repair, with parts and labor commonly ranging from $100 to $250. If the outdoor unit PCB is found to be at fault, replacement board costs can push the total repair cost into the $300 to $600 range depending on the model.