During a defrost cycle, the defrost heater causes the metal alloy in the switch to warm and as … The defrost thermostat on your fridge is an important piece of equipment which prevents your freezer from becoming too cold. The easiest way to do this is to unplug the unit from the wall. However, from time to time, these devices can apparently fail, and cause problems which include leaks upon the floor, a warm refrigerator portion, or a freezer section which has ice forming across the back. This video from Sears PartsDirect shows how to troubleshoot problems with your refrigerator's thermistor or temperature sensor if your refrigerator is not cooling at the right temperature. A defrost thermostat is the temperature-controlling device within the automatic defrost system of a refrigerator. The switch is normally closed. How to Test a Refrigerator Thermostat – A Stepwise Guide. With a freezing refrigerator, this means checking the thermostat itself to see if it is set at the right temperature. Check the easiest and most common potential causes first, which is the best course of action in any troubleshooting case. Directions for testing a refrigerator defrost thermostat. Before you begin to test your defrost thermostat, make sure you disconnect the appliance's power supply. S ome defrost systems use a thermostat (a bi-metal switch) to prevent the defrost heater from overheating. Before you can test the defrost heater you’ll need to unplug the refrigerator freezer and disconnect the wires going to the defrost heater. There are three components to the defrost system: a timer, a thermostat, and a heater. This is because it is the most common cause of major temperature changes in a refrigerator. To test the defrost heater you’ll need to use a @multimeter to do an ohm test. Learn how to test the thermistor to see if it's working. Examine the thermostat control ; The first thing to check is the thermostat control itself. When the coils within a refrigerator become too cold, the defrost timer cues the heater to click on and work to melt any excess ice buildup. How To Test the Defrost Thermostat.