This video shows how to test a common refrigerator thermistor using a multimeter. The thermistor is a temperature sensor. The resistance of the thermistor changes proportionately with temperature. The electronic control board in the refrigerator detects temperature by sensing the resistance through the thermistor.
Use the procedure shown in the video to test the thermistor in your refrigerator.
Note: The resistance value at the measured temperatures may be different for your refrigerator.