LG Refrigerator Error Code R-defroster sensor open

The R-defroster sensor open fault indicates that the refrigerator compartment defrost sensor has developed an open circuit condition. In this state, the control board interprets the sensor signal as reading below -50°C, which falls outside the valid operating range and triggers the fault code. This sensor is a thermistor that monitors temperature at the evaporator during defrost cycles, allowing the control board to determine when the evaporator has reached an adequate defrost temperature and terminate the heater cycle safely.

An open circuit in a thermistor typically means the sensor element or its wiring has lost electrical continuity. At normal refrigerator operating temperatures, the thermistor should present a measurable resistance value to the control board. When the circuit goes open, resistance becomes effectively infinite, which the board interprets as an impossibly low temperature reading, triggering the fault. This can prevent the defrost cycle from functioning correctly, potentially leading to ice buildup on the evaporator over time.

Diagnosing this fault begins with running the refrigerator's built-in self-test function, which can confirm whether the fault is active and persistent. From there, the sensor wiring harness should be inspected for damage, corrosion, or loose connections at both the sensor end and the control board connector. If wiring checks out and the fault persists, the R-area defroster sensor itself should be replaced, as the thermistor element has likely failed internally.