LG Air Conditioner Error Code C1

C1 on an LG air conditioner means the indoor air temperature thermistor has been detected as open or short circuit. The thermistor is a small sensor inside the indoor unit that measures room temperature and sends that data to the control board. When the sensor or its wiring fails, the system cannot regulate operation correctly and displays C1 to alert you to the fault.

Running the unit with a C1 error is not recommended. Without accurate temperature sensor data, the control board cannot properly regulate compressor and fan operation, which can lead to inefficient performance or potential component stress. The system may shut itself down automatically as a protective measure.

A power reset may temporarily clear the C1 code from the display, but the error will return if the underlying sensor fault has not been resolved. Because C1 indicates a measurable electrical fault in the thermistor circuit, a reset alone does not fix the problem. Proper diagnosis using a multimeter to check sensor resistance and connector integrity is necessary before the system will operate reliably.

Some causes of C1 are DIY-accessible, such as reseating a loose thermistor connector or inspecting the wire harness for obvious damage. To properly confirm a bad sensor, you need a multimeter to measure resistance at the thermistor leads, looking for approximately 10 kilohms at room temperature. Replacing the thermistor is a straightforward repair for someone comfortable working inside an air handler, but PCB replacement is better handled by a qualified technician.

Repair costs depend on the root cause. A replacement indoor thermistor is generally a low-cost part, typically in the range of $10 to $40 for the sensor itself. If a service technician is needed for diagnosis and replacement, expect labor costs to bring the total to roughly $75 to $200. PCB replacement, if required, is significantly more expensive and can range from $150 to $400 or more depending on the model.