This defrost thermostat is also known as a refrigerator defrost bi-metal thermostat kit. The function of the defrost bi-metal thermostat is to prevent overheating during the defrost cycle in your refrigerator by protecting the evaporator. The most common sign that there is a problem with your refrigerator defrost thermostat kit is if your freezer is cold but your refrigerator is warm. If your evaporator coils are icy then your defrost bi-metal thermostat kit could be defective.