NTC Sensor Open Circuit — Sources and Solutions
NTC (Negative Temperature Coefficient) thermistors are the most common type of temperature sensor used in refrigerators. An open circuit fault means the sensor circuit has been broken — no current can flow — and the control board is receiving no valid temperature reading.
What Triggers This Error?
The board reads infinite resistance (or an out-of-range high value) from the sensor input, which is physically impossible for a functional NTC thermistor at any operating temperature.
Common Sources
- Broken sensor wire: The thin wire from the thermistor to the connector has snapped, usually at a stress point near a bend or connector.
- Disconnected connector: The sensor harness plug has come loose from the board or an intermediate connector.
- Failed thermistor bead: The ceramic sensing element has cracked or delaminated internally, breaking the resistive path.
- Corroded or oxidized connector pin: Heavy corrosion on a pin creates such high contact resistance that the board interprets it as an open circuit.
Solutions
- Check the connector first: Trace the sensor wire to its plug and reseat it firmly. This resolves the fault in a significant proportion of cases.
- Measure resistance with a multimeter: At 25°C room temperature, most refrigerator NTC sensors read between 5kΩ and 20kΩ. An open-circuit (OL) reading confirms the fault.
- Inspect the wire for breaks: Run your fingers along the wire carefully, feeling for cuts or pinch points. A break will sometimes be visible as a kink.
Replace the sensor: NTC sensors are inexpensive. Match the resistance specification and connector type to your model. Replacement requires no special tools.