I'm no refrigeration engineer. I'm actually an electrical engineer by training. But the way my (now-broken) refrigerator works makes no sense to me. The cooling coils for both the refrigerator and the freezer are located behind the back wall of the freezer. The cold air comes into the freezer and then is circulated throughout the refrigerator using a simple fan. That makes a lot of sense.
The part that doesn't make sense is that the coils get so cold, they freeze up. There's a heater located inside the freezer to heat up the coils to prevent freezing. I've read that, in some cases, the heating element gets so hot, you can actually see it glowing. In my case, there was no glow, as the heater simply stopped working, thereby not allowing the coils to "unfreeze."
I haven't invested the time to come up with a better system, but there must be a better way to architect a refrigerator without using a heater. That just seems completely counterintuitive to me.
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The purpose of the defrosting heater is to melt the ice off the coils that has accumulated due to moisture from opening the door and allowing the warm, moist air to enter. Any ice on the coils makes them less efficient, so you like to keep them clean. Back when I was a young lad (there was a time when I was) you'd have to defrost the freezer yourself by turning it off and maybe placing some hot pots inside. Water would run everywhere and you had a big mess. It was a bit of a pain and you typically wouldn't do it until enough ice built up that the door wouldn't close or you couldn't put anything in the freezer. Freezers were smaller back then, though, because frozen foods were not as popular. Anyway, now refrigerators have heaters that melt the ice off, and then there's a tube that allows the water to collect in a pan near the floor. Warm air from the compressor blows across the pan and allows the accumulated water to evaporate. Simple refrigerators have a mechanical timer to control the defrost cycle, but more expensive appliances have clever units that monitor when the door is open and try to defrost while Mr. Sandman is tugging at your eyelids. Even more sophisticated units try to guess how much ice is on the coils, since running the defroster is a huge waste of energy.
Freezers that are non-self-defrosting still exist, and I actually have one in my garage, Tekochip. You're right about the process of defrosting the fridge manually -- it indeed happens when the door doesn't close. And, yes, manual defrosting is a mess. To fully appreciate the value of self-defrosting fridges, you have to do it manually once.
I'd--thankfully--forgotten about manually defrosting the freezer, and tekochip's description brought back the memories. Uh, thanks? At least they remind me to be grateful for modern self-defrosting machines.
I purchased a backup/extra storage refrigerator to put in my garage last fall. The garage is unheated space. One day in winter, I noticed the garage refrigerator was not cooling - the compressor was not running. After looking at the owner's manual and talking to the appliance service department, I learned that the refrigerator requires an optional heater if it is installed in an unheated space where the temperature may fall below 40 deg. F. This is not the defroster heater which is required to prevent ice build-up regardless of where the refrigerator is installed. Perhaps it is a booster to the defrosting heater? I had never heard of this before last winter. Does anyone know why this optional heater is required for a refrigerator installed in an area where the temperature may fall below 40 deg F? Has this always been a requirement or is this a result of replacing freon with other coolants?
I live in Central Minnesota and it does get a little colder up here, -40C/F is not unheard of. We have a fridge in our barn to store eggs from our hens until they are sold. Like an AC unit a fridge only moves heat from one area to another, when it is below the freezing point things will freeze in a fridge. So every November when the temps finally fall below 32F I simply slip a 9W CFL in the fridge, it generates enough heat in the fridge to keep everything from freezing. And if it starts to warm up beyond the setpoint of the fridge thermostat then the fridge does it's job and moves the heat inside to the outside. I even have to keep my liquid hand soap and other hand cleaners in the fridge during the winter, it's hard to wash your hands with a block of frozen soap! Come April I can finally put out the CFL. Just part of the fun living living in the great white north.
To DW- Ya, up North the compressors get cranky. More so in the new units it seems. My refrigerator/freezer out in the garage quit a couple of winters ago due to the cold. I got a heating tape from the local plumbing supply store, wrapped it around the compressor, and plug it in every fall. The heating tape turns itself on around 40 degrees(F), keeps it all working all winter long.
Tekochip: that's pretty much the same thing my repairman told me. I get it, but it seems to be wildly inefficient.
DW: I also have an old unit in my unheated garage. I'm in NJ, so it gets pretty cold. I hope I'm not putting the whammy on myself, but I've never had an issue with that refrigerator and it has no extra heater.
Here's more than you wanted to know. When I bought my currewnt frig 12 years ago, I sold the old one to the next door neighbor for their garage for $100. They moved, and the new neighbors didn't want it, so we took it back. Please don't tell anybody about the 100 bucks.
@tekochip - yes you are correct the heater is for the "automatic defrost" feature. The simple fridges use a clock motor that triggers a switch that turns on the heater every 24 hours. We use to turn the motor's shaft so that defrosting would take place at night when the familys in bed.
@DW - The optional heater is to keep the refrigerant from turning into a liquid. This prevents damage to the compressor since it is designed to compress gas and not liquid refrigerant. I have split air conditioners and they have these heaters in the ouside compressors that draw many watts of power 24 x 7.
@Charles Murray - Leaving the fridge door partly ajar does not defrost the fridge but actually makes it worst. The fridge will continue to run and actually run longer since it senses a higher than normal temperature. With the door open, outside moisture is drawn in which then forms ice on the cooling coils cutting off circulation. In the end, the cooling coil becomes completely encased in ice ncessitating a manual defrost.
Chipmonger - Maybe it's because I haven't had the need to buy a freezer in a while, but your response to tekochip through me off. A "simple" refrigerator now has a clock too? My "even simpler fridge has the feature you mentioned but without a clock set to it. Periodically you can hear the frost dripping off and being vaporized. At least that is what I've been told that I'm hearing.
Yes it's a clock, sort of. The low model units have a mechanical timer that runs the defrost cycle. The timer can (should) be adjusted so that the defrost cycle happens in the middle of the night when you are less likely to be raiding the ice box. As you move up in models the defrost cycle gets more complicated with units that attempt to know when the best time to defrost is and units that guess when and how long a defrost cycle should take place based upon compressor cycling and coil temperatures.
All frost free refrigerators have heaters to clear the frost off the coils. In the early days, the timer was a clock that ran all the time and the heaters came on whether they needed to or not. There is a thermostat that will shut off the heat once the ice is cleared. Then when the timer cycle is done, the compressor will restart.
Later, in an effort to become more energy efficient, they started making the timer a little smarter. For example, the timer motor would only run when the compressor was running. Now modern appliances have circuit boards and "brains" that try and determine the optimum time to defrost.
For appliances installed in unheated garages/barns. All the cooling takes place in the freezer section (as was mentioned). But the temperature is controlled in the refrigerator section. So if you set it at 40deg, and the garage drops to 30deg, then the fridge will probably not run very often. Not a problem if you are only keeping drinks cold, but a big probably if you are trying to keep meat at 0deg in the freezer.
The extra heater that was mentioned is used to keep the oil in the compressor from becoming to thick and causing damage.
Interesting comments throughout. Several years ago, as a result of having a problem in the sealed part of a home air conditioner, I signed up for a refrigeration class at a local community college. Stayed long enough to get an associates degree! Most interesting, and they covered numerous topic including refrigerators and freezers as well as the various designs, and ended in commercial HVAC systems. When taking the last "hands on" test, the instructor had me scheduled last. He then told me I did not have to perform the exercise, as even if I failed I would still maintain an "A". But he asked me what I did for a living and I told him I was an engineer and designed electronics for a big DOD contractor. When he asked why I was there, I told him I wanted to be able to fix a bad AC I owned! "You spend two years and a ton of your own money to fix an AC?" "Yep", I replied. "No such thing as wasted learning." Like Neo in the Matrix; "I know Kung Fu!"
Yes the refrig uses a timer on a cam to drive a microswitch to set the defrost cycle and their failure is the most common problem in older units. Newer ones are starting into solid state timers and triacs rather than mechanical switches. Even my Maytag washer is mostly solid state, but has a motor driven knob controlled by the micro. Sort of retro in design.
Everything is simple when you know how it works. It has taken me nearly 70 years of learning to get to this point. Still have lots to learn. Life is a journey indeed.
But now you know some Kung Fu! At least as far as your frigerator.
Ditto, Al.. Did not think there could be two individuals of such similarity. I am 78 y/o and still learning everyday. I also an EE that ended up doing most of the negotiations for our company and went back to law school at nights for the primary purpose of having a better understanding of contract law. Ended up 4.5 years later with a JD degree.
By any chance did you work with me on a blimp project in the Florida Keys several years ago? Then again maybe there are more than one old EE/lawyer combos around, as strange a combo as that might sound. Looking backward from the present my life has been nothing short of wonderous and filled with wonderful and interesting (for the most part) people. No way can I ever stop working.
Fraid not Al but it surely would have been my pleasure. I live in Oregon now but spent most of my career working in So Calif. Gen Dynamics, Pomona; General Electrodynamics, Pasadena; Lockheed Electronics; Leach Controls; Philco Ford Semiconductor; Odetics and then private law practice.
Used to be you had to empty the fidge every so often to defrost it. Those fridges had a small freazer section and it would collect the frost out where you could see it.
Newer designs offer much more freezer space and efficiency and thus the coils are moved out of sight so you don't see the frost collect.
The only way around it is to not open the fridge/freezer as the source of moisture for the frost is from the air you let in every time you open the door.
Under certain conditins of high humidity the frost can collect at such a rate than the defrost cycle is unable to clear the buildup of ice. Then the only way arond it is to either empty the fridge/freezer and allow it to warm up and melt the ice, or remove a panel(if possible) and use your shop vac to blow the warm house air on the frozen section and defrost the fridge. I have had to do that operation 2 times, both at times of very high humidity. And afterwords the 2 different units worked fine.
One way to reduce the frost build-up would be to fill the freezer with a dry gas, such as dry nitrogen, with a slight positive pressure relative to the outside air. Air would still enter the freezer when the door is opened, but frost build-up would be greatly reduced. The drawbacks? Gas consumption and risk of suffocation.
Another possibility is to use heat-pump technology to defrost the freezer, either by using a separate refrigeration loop, or by reversing the one that is already present. This would be more energy efficient than a resistance heater. The drawbacks? Cost (of the additional mechanical equipment) and reduced reliability.
What you may not know is there may be two other heaters in the refrigerator/freezer. Icemakers have heaters to get the ice to release from the ice mold. If that heater is not operating, the ice maker will have ice in it but will not cycle. The ice eject/water refill cycle will start and stall mid-cycle as it would normally do until the ice would slide free from the mold. With no heater, the ice will not slide and the icemaker sits stalled. The icemaker's motor is designed to stall in this manner.
The second heater is around the door. This heater is to eliminate condensation outside the cabinet around the door gasket if the unit is used in a high humidity location. It usually has an operator switch to disable the heater is condensation is not as issue.
The knob is the perfect user interface! It tells the user what point of the cycle is being executed and you then turn the knob to inform the machine that you want a different part of the cycle. It's tough to design a control to drive the knob as a display device and then use its position as an input device, but this is really the perfect user interface. I worked on one of these hybrid controls and it was much more expensive than a cheap membrane switch, but was far more intuitive. Interestingly enough, the White Goods manufacturers used to give us timing charts from mechanical timers and that was what we would write code around. The OEM was so used to working in the world of mechanical timers with cams and switches that they couldn't let go of designing with that type of documentation. We eventually wrote a tool that allowed the OEM to create a timing chart on their PC and the tool would then create a cycle table in C for our micros to run from.
Thanks for the reasoning behind the knob. I'm still disappointed that they use such a mechanical unit however since LEDs and display unit prices have plummeted. When I turn the knob, I still hear the cam and switches clicking away. Yet in spite of the new technology, the only failure I have had in the Maytag was the upper computer board, not the knob. Another microproc runs the variable freq for the 3 phase motor on the drum. After having the upper control micro fail I expected the lower one to fail next. Nope, the next failure was the drum support bearing. Not only did it fail, but I had to buy a new drum as the bearing was cast into the assembly! I guess "new" does not always mean "improved". Along the same lines I bought an old time double edge razor to shave with. Much nicer than the 3, 4, or 5 blade with or without Aloe, etc. I recommend these razors highly since switching. Sort of a "saving face" thing. Thanks for your input.
Refrigerators may also use efficiency robbing heaters to keep the water supply to the icemaker from freezing, and to keep condensation from the door seals. Pull a schematic on a modern unit (Particularly a high end unit.) and you'll be surprised.
(Oops, I see someone scooped me on this observation.)
After I bought my Viking refrig several years ago (old analog controls) I had problems with the water feed to the icemaker: it used to freeze up near the dispense end. I had to drop the icemaker out of the way and squirt hot water down the fill tube. I found out later that the Sub-Zero brand has a heater on the supply tube. For an unknown reason the tube has not stopped up in about 2 years: very strange. Its probably all the clean living.
There are some units for sale in the US, and of course in Israel, that have circuits designed for compliance with rules for the Sabbath. Jewish law (as I understand it) says that one must not kindle a flame during the Sabbath, and this has been interpreted as not doing something that would actuate an electric circuit. Thus an observant Jew must not turn a light on or off. Putting the fridge in Sabbath mode disables the light switch, but also changes the compressor/thermostat function. It does not go on based on temperature, because then opening the door would cause it to warm up and trigger the ciruit. Instead, a random timer turns the ocmpressor on and off. More sophisticated units observe the recent cycles and "learn" how much the compressor cycles and emulate that timing.
My garage freezer is half-size, about 4 feet high, and needs periodic manual defrost. My clever approach to save time is to empty it, then use my heat gun to speed thawing. During the last defrost challenge, I learned that the heat gun is hot enough to melt the interior plastic liner. This gives me the advantage of inspecting the insulation through the hole! Great new feature!
Try a hand-held hair dryer the next time..... not hot enuf to melt plastic, but more than warm enuf to melt ice, and a heck of a lot more convenient than chugging over pots of hot water for hours on end.
There has been much discussion on the energy use side about the heaters in refrigerators (coil defrost and ice tray) and how much energy that the heaters use versus the more efficient compressors and controls now in modern refrigerators. This will become a greater focus of the save energy forces in the future so expect to see some alternative solutions.
On the consumer side most people today do not have a clue that refrigerators have heaters in the unit.
As for refrigerators in cold environments, most have warnings about this issue in the user manual but, as we all know, who reads a manual.
"Got to have it out of the box NOW, NOW, NOW!!! and plugged up NOW, NOW, NOW!!! and have/make it work NOW, NOW, NOW!!!"
(Many times I have helped family members, coworkers, neighbors with some sort of new appliance or machine set up, assembly, etc problem by my actually referring to the item's included manual in a methodical and calm manner even to the point of exasperating the person who asked for my help.
My attitude is "tough" - if you are too impatient, lack mechanical ability, or lack troubleshooting ability then your feelings are not my problem when you ask me to help with solving something that just following the manual instructions could have avoided.)
There is a timer which periodically turns off the compressor and powers up a defrost heater in series with temperature sensing switch which opens at a relatively high temperature (65degF maybe) and closes at a very cold temperature (-40degF maybe). So when the timer applies power to the series heater & temp switch, the heat melts the ice until the switch warms up to the turn off point. Sometime later the defrost timer again activates the compressor plus in-box temperature controls.
The usual failure mode is that the defrost temperature switch does not properly switch on at very cold due to drifting lower temperature switch point (say -50degF). As a result, the heater never turns on to defrost the coils and the moisture builds up until the coils are clogged. To confirm, locate the defrost timer (sometimes on bottom of refrigerator or may be inside somewhere), use a screwdriver to advance the timer into defrost mode, and then short out the defrost temperature sensor (Maybe you do that with the power off) to see if the heater comes on. If so, solution is to replace the defrost temperature switch.
My defrost heater worked so well it was flooding the fridge compartment because the regular drainpipe where the water should flow out and evaporate would occassionally freeze shut and backup. I eventually discovered attaching an appropriately sized piece of soda can from heating coil to just inside drainpipe solved the soggy vegetable problem. I later found such a solution on Amazon.com as well fo rmuch more money than my AL can and self-tapping screw. This design flaw continues to sell many fridges.
Once upon a time, long, long ago, products were designed and manufactured to be functional and reliable for long life and use. Today, quality and reliability have been sacrificed to bring costs down, increase corporate profit, and to increase future sales by designing planned obsolecence, while retail prices are out of sight. My first Frigidaire fridge/freezer purchased in 1960 lasted over 35 years with only 2 noisy freezer fan replacements; my first Matag washer (1960) lasted 33 years with 1 timer & 1 water pump replaced. etc, etc., Ah, for the good old days before going green and household appliance computer automation that is programmed to inefficiency and premature failure ahead of it's time... One cannot buy a cheap repair component anymore -- you have to buy "an assembly" because no-one troubleshoots anymore --- but that is a subject for another post...
For industrial control applications, or even a simple assembly line, that machine can go almost 24/7 without a break. But what happens when the task is a little more complex? That’s where the “smart” machine would come in. The smart machine is one that has some simple (or complex in some cases) processing capability to be able to adapt to changing conditions. Such machines are suited for a host of applications, including automotive, aerospace, defense, medical, computers and electronics, telecommunications, consumer goods, and so on. This discussion will examine what’s possible with smart machines, and what tradeoffs need to be made to implement such a solution.