Real World Domestic Refrigeration
If you browse around the internet you will find bucketloads of websites that will tell you how a fridge works, a freezer works or a fridge freezer works but, when you read them, they will all say pretty much the same thing and explain the basic premise of a simple heat exchange along the lines of a heat pump. Essentially this is totally correct in every way and is how a domestic fridge will work, what it almost always totally fails to explain is the control systems which are far more prone to failure or how to practically diagnose a fault on a fridge or freezer. I would suspect that how to find the fault is the main reason that people look this sort of information up as, beyond that, few people seem to really care how a fridge works.
In this lengthy article I'll deal with how fridges work outside of that comfort zone and then split off into different articles that will relate to each individual product type as there are marked differences between them. However you may find much information copied to each from this core document that relates to each product type.
The Basics, Refrigeration 101
The first thing that you or anyone interested in refrigeration has to know is the point of it. Ask most people and you will get a reply like, refrigeration is to keep stuff cold and, whilst this is perhaps true it is not accurate.
The point of refrigeration is to keep items (whatever they may be) within the cabinet at a stable and constant set temperature irrespective of the external (ambient or room) temperature.
It is very important to remember this point.
The external, or as I will now correctly refer to it, ambient or room temperature, is really irrelevant in many ways and vital in others. You see the ambient will dictate how hard the refrigeration unit must work, the thickness of the insulation as well as a few other things you really don't need to know or care about. Just please do me a favour, when I talk about the ambient being within a range or whatever just take what I say at face value, accept it and don't argue.
It is worth noting that most modern fridges and freezers are designed to work in a temperature range of +15°C to about +31°C, stray outside this, for example keeping a fridge or freezer in a cold garage, and you are asking for trouble.
The idea of refrigeration is to keep this ambient temperature irrelevant and to maintain the "ideal" food storage temperatures within the confines of the cabinet. I repeat it so you get it as people forget or ignore the fact that refrigeration is much like cooking, the exact opposite in what you are trying to do though, but both are about temperature stability. If you lose that stability then it doesn't work properly and, when you are going to consume food on the premise that it has been stored properly and is as bacteria free as you want, then temperature stability is absolutely paramount whether cooking or cooling.
With that said what manufacturers use is a "mean" temperature or an average, so you can get fluctuations but the mean should be as follows but do please note that these are ideal temperatures and I will explain each.
Frozen food: -18°C
Frozen food degrades at its lowest level at this temperature thus maximising the time that the food can remain frozen.
Chilled food: 2-5°C
Chilled food would be the likes of milk, dairy products, fruit, vegetables and suchlike, the normal stuff yo u bung in the fridge.
Chilled meats: -1-2°C
Chilled meat is fresh meats, delicatessen meats, pate and the likes. You don't want it to freeze but storage at this temperature will maximise the life of the food.
Should you venture outside these temperature ranges then the food will degrade faster than it should and you may risk eating contaminated food as biological cultures grow inside the food causing degradation to it. This degradation we will often see as "rotting" and smell which is out natural defence against eating something that has gone "bad" but, that instinct is not infallible especially with meats and fish. If, on meats and fish especially you wander outside the correct storage conditions then you are liable to create the conditions to grow salmonella, listeria and many other bacteria or disease that, really, you don't want and this is why temperature stability is absolutely paramount in refrigeration.
One point to make is, don't trust the cheap fridge thermostats you can buy at the local supermarket or whatever as they are notoriously inaccurate. We tend to use infra red digital thermometers these days that give a true and accurate surface temperature and, whilst this does not give us a core temperature of the food it does give us a very good idea of the actual storage temperatures.
Fridge And Freezer Insulation And Door Seals
This is often the most overlooked part of refrigeration and it applies to all machines.
You have an area inside the cabinet that you want to keep at a set temperature and, outside of that you have yet another temperature that will be the ambient. The ambient is what the fridge or freezer is fighting to keep out whilst also battling to keep the set temperature (usually much lower than ambient) in the cavity. All that stands in the way of the two meeting is the insulation and the door seals and, this is also very important when you buy a new fridge or freezer.
The poorer the door seals quality and actual seal is, the more ambient temperature gets in and the harder the fridge has to work to keep the contents cold. The same goes for the insulation. So, when you buy a new fridge or freezer do look very carefully at the climate class as this gives an indication of how good the machine stands up to abnormal temperatures and also make sure that the seals look good and solid as well as the walls of the cabinet being nice and thick. Many manufacturers will cut corners on both to get fridges and freezers made cheaper and, you get what you pay for.
In general, the better the climate class (the larger range of temperatures it can accommodate) the better the unit will be sealed and insulated.
If you get a ball of ice on a fridge wall for example or outside the actual cabinet then it is almost certain that the insulation is goosed. That being the case the best thing you can do is put it down to experience and go shopping for a new one. Insulation repairs are both time consuming and in most cases unsuccessful. It should be noted however that there are other things that can cause an ice ball on the inside on some machines so it is worth asking about it in the forums.
Refrigerant Gas In A Fridge Freezer
This is where I start to burst some myths.
No doubt, if you have a fault on your fridge or freezer, you've likely ferreted around the internet and seen that a refrigerant gas is used to form a heat exchange or simplistic heat pump swapping hot for cold gas and you'll know that the cold is low pressure gas, the hot a high pressure. Fine, but what good does this new found knowledge actually do for you?
You now know how it works in theory but, in practise?
The fact is that in mot all domestic fridges and freezers the there is a "compressor" which compresses the gas and pumps low pressure cold whilst brining in the hot high pressure gas on what we refer to as the hot return line. So what?
In all honesty unless you have a vested interest in knowing how a fridge works and want to understand Boyle's Law and a host of other things that you really don't need in your head, you don't need to know.
What You Do Need To Know About Refrigeration Systems
The first thing you need to know is that refrigeration is a closed and sealed system. If it becomes open and the gas escapes, it will no longer work. Full stop, end of story.
This video shows how the refrigerant system works, the various parts inside the fridge compressor and so on show the basics on hos a modern refrigerant system works mechanical as well as the gas flow very clearly and well.
If the system had a leak from new then it will fail within 12 months easily, modern iso-butane systems will show a fault if there is a leak in a matter of weeks at most, if not days. If someone tells you that your 2 year or more fridge has suddenly developed a leak then either they don't have a clue what's actually wrong with it or it has suffered from physical damage. Gas does not leak from a closed system without someone or something making a hole for it to escape from.
Stab it, break it, kink pipes, break pipework or any other physical damage to the "evaporators" or "condensers" and it will be rendered knackered. Often not because it has lost the gas charge but more because moisture in the air has entered the system and contaminated it then subsequently "choking" the system. This happens because the moisture forms droplets that effectively stop the gas from circulating correctly given the very fine diameter of the pipework.
If none of the above apply to the failure then it probably isn't a system fault as such. The only moving parts are the compressor itself which is essentially an electric pump in most cases or heat in ammonia based systems (these are rare now) and a "diversion valve" (well, I call it that anyway) where they are fitted. The only other moving parts are cooling fans where a large compressor is used and also air valves which are common in American or American style fridge freezers.
However, it is fair to say that most faults that occur outside the warranty especially will be to do with the control system and not the refrigerant system. Compressors can and, do, fail though and if you hear a repeating "click, buzz" then it's likely that the compressor has failed.
Fridge And Fridge Freezer Control Systems
There are basically two ways by which to control a fridge or freezer, either electro-mechanically (the old way) and electronically (the new way) and there are pros and cons for each.
The Old Electro-Mechanical Method
This would be old thermostats with a phial that is filled with a gas. The gas expands and pushes a simple pressure switch that switches off the compressor then, as the unit heats up again the gas contracts, the pressure decreases and the switch is released allowing the compressor to once again run.
It's really dead simple stuff at the core of it.
When thermostats fail they will either fail closed, that is to say that the compressor will run continuously and the unit will overfreeze or fail in an open position where the compressor will not run at all.
The real advantage in these systems is the simplicity of them and, as they are using decades old technology, they tend to be very reliable. The downside is that they are not as accurate in maintaining a set temperature and can vary easily by up 10-15% and sometimes more than the set temperature.
The New Electronic Way
This is more complex.
The unit will use a PCB (Printed Circuit Board) to control the run times and monitor the cabinet's temperature using thermistors that, as the temperature changes their resistance changes. This change is detected by the electronics which then act depending on the logic programmed to the control board.
That sounds easy doesn't it?
In theory it is, but manufacturers will program allsorts of crazy fault codes into these boards then not give you a clue as to what they actually mean, a lot like many other appliances these days, which leaves you out on a limb when things do go wrong. You will also, like us, not know what the resistance range of these thermistors should be, you have to work it out.
And, without that information, is it the board or is it a thermistor fault?
Mostly these systems are used on frost free machines so you have at least three thermistors, the fridge one, the freezer one and at least one defrost one to monitor the defrost heater temperature. On and, if the defrost heater goes faulty, yep, you get a meaningless error code and a dead fridge.
The error codes also cannot often take account of physical problems, such as ice build up blocking a fan motor or an icemaker jammed by a lump of ice so do try to check for obvious things before calling an engineer.
The thing is that the manufacturers are actually correct, these new systems are far more accurate and do offer better temperature stability. The cost is that you introduce more things that can and, do fail. This is especially so with frost free fridges and freezers as the more features packed into them such as individually controlled temperature zones, icemakers and the likes then the more complex they become, the more components and the more there is to go wrong.
Diagnosing Problems On Fridges & Freezers
As you have by no doubt now realised there are a myriad of different control systems, electronics and ways that refrigeration of your food is carried out and this is largely to do with the method of temperature control as, in principal, barring absorption units used in boats, caravans and so on, the actual method used to cool the air inside the cabinet is pretty much all the same. Sure, we have falling air and blown air, but that's about the only real difference.
So when you get a problem, especially after a few years service, the actual refrigerant system is most likely the last thing that will go wrong. The technology is, by today's standards, antique and generally very robust as well as extremely well proven.
What does fail a lot is thermistors, electronic control boards and defrost heaters. These are the single most common parts that fail in modern refrigeration and can throw up all sorts of weird and wonderful faults and these are where you should start looking for failures. The problem is, they are not always obvious to find nor easy to diagnose the problem on and, given that if you make a mess of it you can give yourself food poisoning, we can hardly recommend that you engage in guessing at what's wrong.
However if you sit and read this article carefully as well as others on the site you will understand what the machine is trying to do in general and you should be able to figure out how it goes about it with a little thought.