Basic Defrost System In your Refrigerator
The defrost cycle has failed to function. There are three major components which make up the defrost system. They are the defrost timer, defrost heater and the defrost terminator.
Let me explain the defrost timer. It is about the size of a package of cigarettes. There are male electrical terminals which control which cycle the defrost system is in. The first cycle is Cooling where the compressor is running or is satisfied by the thermostat. We will call this the cooling mode. The second cycle would be the defrost cycle. In addition to the usually four male terminal connections, you will find a motor. Depending on the type of defrost timer you have, this motor could be internal or on the outside and usually silver or copper in color. This timer is just like an alarm clock. In most instances, the timer is always running. There are exceptions to this, but we'll get into that later. Every so many hours, usually 6, 8, 10 or 12 hours, this timer, set by the manufacturer goes off. When it does, contacts inside the timer turn off the compressor and turn on the defrost heaters for a certain amount of time. Your defrost heaters are located in the freezer section and connected to the cold evaporator coils. When electricity coming from the defrost timer activates the defrost heater, it becomes hot (VERY HOT) and melts the frost buildup from the evaporator coils. This defrost cycle can last up to 35 minutes. On the other end of the scale, about 15 minutes is the minimum. Let's go over what we know so far. The defrost timer is the brain, so to speak. It controls the refrigerators defrost cycle. This defrost timer turns on the defrost heaters. Once the heaters are supplied with electricity, they become hot (VERY HOT). The defrost timer continues to advance (Like a clock) and soon advances long enough to turn off the defrost heaters while at the same time, turn on the compressor (if the thermostat or cold control is not satisfied). What I mean here is if your refrigerator is cold enough, when the defrost timer advances to cooling or turning the compressor on, your compressor will not come on. If at this time you would turn the thermostat up a few notches, then the compressor would come on.
The defrost heater and in some cases, heaters, are actually heating elements. There are three types of heating elements and literally 100’s of shapes and sizes which have been produced over the years. Whether your heating element is glass tube, calrod or aluminum it functions the same. The Calrod heating element is made up of the same type of material used to make burner and oven elements on electric ranges. The Glass Tube heating element has a coil of wire inside to produce the heat and glows red hot when 110 volts is applied to it. The aluminum colored heating element has a small tightly wound coil inside, much like the glass heating elements to produce the heat. The only function of the defrost heaters is to melt the frost on the evaporator. These can be tested with an ohm meter. If there is not resistance, the heating element is bad.
The defrost terminator is a small factory set thermostat which terminates the defrost cycle when the temperature in the evaporator section reaches a certain temperature. This defrost terminator is wired in-line with the defrost heaters. It is about as round as a quarter and about ¾ inches thick. You will see two wires protruding from it. The operation of the defrost terminator is really simple. When your refrigerator is in the cooling mode, the defrost thermostat closes. When the defrost timer advances to the defrost mode, the defrost terminator is closed, thus allowing the flow of electricity to pass on to the defrost heater(s). The defrost timer is designed from the factory to remain in defrost for a predetermined amount of time by the factory. For conversation sake, lets say your defrost timer has a 8 hour 21 minutes cycle. What this means is that every 8 hours the defrost timer will shut down the compressor and turn the defrost heaters on for 21 minutes. If you haven’t opened your refrigerator all day long, the frost buildup in the evaporator section does not need a 21 minute cycle to defrost the frost buildup. What happens in the evaporator section is the heat begins to build up. Again for conversation sake, let says your defrost terminator is rated at 55 degrees. So, when the temperature in the evaporator section reaches 55 degrees, the defrost terminator opens and stops the flow of electricity to the defrost heaters thus stopping the defrost cycle even though the defrost timer has not yet advanced far enough to switch from the defrost cycle to the cooling cycle.
This cycle is repeated over and over again until one of the components fail and frost builds up on your evaporator. Got more questions? Email us at firstname.lastname@example.org