LG Refrigerator Error Code F-defroster sensor open

The F-defroster sensor open error on an LG refrigerator indicates an open circuit fault in the freezer area defrost sensor. This sensor monitors temperatures during the defrost cycle and reports back to the main control board. When the board reads a sensor value below -50°C, it interprets this as an implausible reading and flags the open circuit fault. An open circuit means the electrical path through the sensor has been broken, preventing any valid temperature data from reaching the control board.

The freezer defroster sensor is a thermistor, a resistive temperature-sensing component whose resistance changes predictably with temperature. Under normal operating conditions, the sensor produces a resistance value that corresponds to a real temperature within the freezer's expected range. When the circuit is open, resistance becomes effectively infinite, which the control board translates as a temperature reading below -50°C. This triggers the fault code and may disrupt normal defrost cycle operation, potentially leading to frost accumulation on the evaporator coils over time.

The most reliable way to confirm the fault is to run the refrigerator's self-test or diagnostic function, which cycles through system checks and can isolate the sensor fault. If the self-test confirms the open circuit in the F-area defroster sensor, the sensor should be replaced. Technicians should also inspect the wiring harness between the sensor and the control board for breaks, corrosion, or loose connector terminals before condemning the sensor itself.