What you probably didn't notice was that the freezer has not been going through it's normal defrost cycle. Because of this un-noticed event going on, there has been frost building up on the evaporator coils that doesn't belong there.
After this frost continues to build up over the course of a few days to a week or so, now you are going to start to notice the effects. Let me explain the defrost system in general so you get an understanding of what is going on.
The coils inside the freezer are the only part inside the whole refrigerator that "get cold". They need to stay free from excess frost build up so that air can pass through the coils and reach the refrigerator section of your refrigerator. Every eight hours or so, depending on the type of defrost timer or control you have, the compressor and fans will shut off and the machine will go into defrost mode. When the refrigerator is in defrost there is a heater that is tied into the evaporator coils inside the freezer that comes on.
This heater is behind the rear panel inside the freezer where the evaporator coils are located. It melts the frost that has accumulated over the course of time. After about thirty minutes the machine comes out of defrost and goes back to normal operation. Now the air can continue to pass through the coils and keep the freezer frozen and the refrigerator cool and everybody is happy.
Some refrigerators have a defrost timer. This type works like a clock. Every eight hours or so the machine hits the defrost spot and that's when defrost occurs. Some refrigerators have an Adaptive Defrost Control. This is what makes a refrigerator energy efficient. It varys the length of time it takes the machine to go into defrost. So instead of the energy hogging heater coming on every eight hours, it may be 24 hours, 18 hours, It depends on how many times you have opened the doors, how long the compressor has run.
This is good because the refrigerator may not need to go into defrost every eight hours. Now you are saving energy. Good Stuff. This is the component that controls how long the heater stays on when the machine is in defrost mode. At room temperature it will usually be open which is normal and not a sign of being defective and only close when it gets cold. How cold it has to be to close will depend on its particular calibration but usually near or below freezing point.
Some newer model refrigerators Amana and Frigidaire in particular and some older models GE included run power for the evaporator freezer fan motor through the defrost heater element and defrost limit switch. If either of those components should fail, remaining open, the fan will not run which will stop the circulation of cold air throughout the refrigerator. On that design, the evaporator fan motor will not start running after a defrost cycle until the evaporator has had a chance to begin cooling again.
While it is generally a good design idea so as not to blow the warm defrost air throughout the refrigerator, a failure in one part of the defrost system will usually render the whole refrigerator ineffective because of the lack of air flow. Early production mechanical defrost timers would go into the defrost cycle after a set amount of time. Common timing periods were 6, 8, 12 and 24 hours. This meant that say every 6 hours, the refrigerator would go into defrost whether it needed it or not.
The duration of time it would remain in the defrost cycle was fixed and could be anywhere from 18 to 30 minutes depending on the timer design but it would always be the same length of time. As stated above, the defrost heaters may not be on for that full length of time, thanks to the defrost limit thermostat, but the cooling cycle would not start again until after the complete defrost duration was ended.
This original design was wasteful as the refrigerator would defrost regardless if it was necessary or not. A later design tried to help this a bit. The next design was called a 'cumulative run' timer. These timers were installed in a way were they would only count the time that the refrigerator the compressor was actually working. This makes sense since no frost could build up if the compressor was not running. These later mechanical model timers would only advance the into defrost when the compressor had actually been running for a certain length of time, usually 6 to 8 hours of accumulated compressor operation.
The latest, energy saving variation is electronically controlled and called an adaptive defrost control. Not only does the period between defrost cycles change but also the time duration of the defrost cycle itself. The device is programmed to keep track of the appliance usage and how long it takes for the evaporator coil to be thoroughly defrosted. It will then calculate the amount of time required and adjust itself accordingly. Newer GE made refrigerators are almost totally electronically controlled.
Their motherboard takes the place of both the temperature and defrost functions even controlling DC fan motors that can operate at several different speeds. On this system only the defrost heater is the same as described above. A defrost cycle is ended when a thermistor detects a temperature rise of the evaporator which is the signal to the main control to terminate the defrost and start the cooling. The termination thermostat on this appliance design only acts as a safety device to shut the heater s off in case of a malfunction before the plastic interior liner melts, otherwise it is never active.
The control can not be manually put into defrost mode. The mechanical timer types described above will usually have a screw on their underside which can be turned clockwise to manually change its present cycle.
If running, slowly turning it until it clicks once should put the timer into 'defrost mode'. When in the defrost mode, turning it until it clicks once should put the timer into 'run mode'.
It can be left in the defrost mode to see if it will advance by itself to the run mode like it should in less than 30 minutes or the defrost heaters may be able to be tested to see it they are receiving power or not at that time.
NOTE: Once the compressor has been turned off, it should be allowed to sit idle for several minutes minimum before attempting to restart it. Known as auto-defrost or self-defrosting , this feature is essential for controlling the frost inside refrigerators and freezers.
While most people are familiar the general concept of auto-defrost, few people know how the system works. The ice acts as an insulator, making the refrigerator work twice as hard to try and stay cool. Defrosting solves the problem of ice build-up on the evaporator by melting the frost.
When the atmosphere surrounding the frost-covered evaporated rises above 32 degrees Fahrenheit, the frost will begin to melt. Some of the early model refrigerators required manually defrosting by disconnecting power to the unit for a given period of time. Thankfully, most modern-day refrigerators and freezers have an auto-defrosting function. Refrigerators and freezers with auto-defrost usually have a temperature control mechanism that tells the unit when to stop cooling.
Of course, there are also some disadvantages to auto-defrost as well. Due to the increased complexity of its mechanical components, repairs and maintenance on auto-defrost refrigerators are more difficult.
Hopefully this will give you a better understanding of the auto-defrost function in refrigerators and freezers.
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