The freezer worked fine for a while and then stopped. How Do Defrost Bi-Metal Thermostats Work? Defrost Thermostat. According to Appliance-Repair-It, the evaporator thermistor is attached to the top of the refrigerator coils in the freezer. If it still does not read within limits, it is most likely defective. What Should I Consider When Buying a Used Freezer. A thermostat is an open and closed switch, they are usually round in shape like the one shown above and they open within a set temp range and they close within a set temp range. The duration of the heat cycle is controlled by the timer. It is attached to wire plugs near the coils of the defrost system, and connected to a wiring harness that will allow for its removal. This switch operates the heater. Once the defrost termination thermostat (a.k.a. It is basically when water turns from a solid to a gas without going through the liquid stage. The small freezer that is attached to our refrigerator is not nearly big enough for our needs. If the defrost thermostat stops working, frost forms on the evaporator fins, and the temperature in the freezer rises. I was always clueless about how a freezer defrosted itself as well. Not more than a month after we got it, I noticed a giant puddle of melted ice cream on the bottom. It's because inside every one of these appliances is a heater. @jcraig - I think I actually heard the answer to your question a couple of weeks ago. How To Test the Defrost Thermostat. Typically located underneath the refrigerator, the defrost thermostat may alternately be found in the back of a side-by-side refrigerator/freezer. The sole purpose of the evaporator thermistor is to control the defrosting cycling. If you have ever defrosted a freezer you know what a pain this can be. S ome defrost systems use a thermostat (a bi-metal switch) to prevent the defrost heater from overheating. This was a brand of refrigerator/freezer that I had never used before, and I won't be buying another one. As long as that defrost thermometer keeps working I know that I won't have to defrost another freezer again. Anyway, if you ever feel the side of your freezer sometime, there will be a very thin layer of ice, but at some point, it sublimates and disappears. By the time I got home, most of the food in my freezer was ruined. When the circuit closes again, it will then cool off the metal. Scraping it never seemed to help either, and there always warnings that using something like a screwdriver or ice pick could puncture the wall and ruin the freezer. Enough sublimation happens to get rid of water that there is never any ice that stays left over. There are three components to the defrost system: a timer, a thermostat, and a heater. It is basically a process called sublimation. Most people have only positive things to say about them, but this hasn't been the experience for me. Understanding Defrost Cycle . Does anyone have any idea how often a defrost cycle happens in a normal freezer? So far I have not lost my food because of this, but I know I have to watch it closely. Thankfully I purchased a warranty on them so have not had to spend a lot of money on appliance repair, but I am worried what will happen once the warranty runs out. The heater is on the bottom of the evaporator coils and the defrost thermostat sits on top of the evaporator coils. These digital boards replace the traditional mechanical defrost timers and thermostats, and plug directly into the refrigerator. The defrost control board is located in the control box. This heater melts any frost before it can accumulate and evaporates the moisture away. This property is used to make a switch which opens with a temperature change. If the high limit thermostat is open at room temperature, the refrigerator's defrost system will not work. First you have to take everything out of it and wait until all ice that has built up melts. Ever since then I have not kept a lot of food in the freezer because I don't feel like I can totally trust my freezer to work right. When all the ice melts down, the temperature of the back panel of the fridge starts rising. You could run the defrost setting, but then you ran the risk of ruining your food. Wikibuy Review: A Free Tool That Saves You Time and Money, 15 Creative Ways to Save Money That Actually Work. The sensor should have a resistance of 5 Kohms at room temperature. This property is used to make a switch which opens with a temperature change. Modern, frost-free, auto-defrost refrigerators consist of a confusing network of colored wires. When my defrost thermostat in my freezer quit working I was gone for a long weekend. A defrost thermostat is the temperature-controlling device within the automatic defrost system of a refrigerator. This component is responsible for controlling the time duration for the heater to stay on during the defrosting process. Like someone else mentioned, that's really counter-intuitive as to what you would initially think. It is called a bi-metal thermostat because at its heart is a strip made of two metals with different expansion rates, which when heated begins to curve. I have not had to replace the defrost thermostat yet, but wonder how hard that is on it every time something like that happens. For instance, in a defrost cycle of thirty minutes, the heater only stays on for a period of ten minutes. I remember the first apartment I lived in had one of the older freezers that didn't defrost. Even if there is actually no frost present the defrost cycle takes place. In the past, my extra freezers have been upright freezers that did not automatically defrost. When this happened it was necessary to remove everything from the freezer and melt the ice away. Working in conjunction with a timer the defrost thermostat controls the heater which turns on briefly when the bi-metal strip closes the circuit. This device works to measure internal temperatures and prevents the refrigerator from becoming too hot or too cold. I didn't really understand the science of how water can go straight to a gas form, but apparently it happens a lot in freezers. Many newer-model refrigerators feature adaptive defrost control boards.