A Guide To How Freezers and Fridges Work

How Fridges and Freezers Work

Apart from the odd few, most people are not that interested in how refrigeration systems work, other than to try to understand what is causing a specific problem with their own appliance.

In very basic terms, your domestic refrigeration appliance is controlled by a simple heat exchanger along the lines of a heat pump.  However, with modern fridge freezers, technology is now much more advanced and, especially the double door American style fridge freezers, are far more complex.



Importance of Refrigeration

In order to keep your stored food in as fresh a condition as possible within the refrigerator requires a steady temperature of: 

2-5oC for cheese, fruit, salad etc.

-1-2oC for meat, fish etc


In modern refrigerators, there are usually various chiller drawers and boxes which will provide the required temperatures for your specific foods.  A lot of people have a tendency to overfill their refrigerators, especially on a big shop day, but it is worth taking the time to ensure you have stored the correct foodstuffs in the right compartments. This will give you the best shelf life of your food and will avoid early degradation.

-18oC is the correct temperature for your frozen food in the freezer

The outside or ambient temperature of a fridge freezer is more or less irrelevant, the most important function is to keep the temperature within the various cabinets of your appliance at the correct temperature to keep your food safe.  Most appliances are designed to work within an ambient temperature range of +15oC to roughly +31oC, working on the assumption that your fridge freezer will be located within the house itself.  Keeping this kind of appliance in an outhouse or garage can lead to problems, as temperatures can obviously move outside of this tolerance.

Temperature stability is obviously the key to keeping your food stored safely and to avoid the introduction of bacteria and salmonella into the family’s diet – not to be recommended!

Some people rely on the cheap thermostats that are available in supermarkets, but they are generally not very reliable and could give a false sense of confidence that everything is working correctly.

Door Seals and Insulation

As with all appliances, you should aim to buy the best product available within your budget.  This doesn’t always mean the most expensive, and time spent in research is well worth it.  Although the shiny surfaces are very appealing it could mean the manufacturer has spent more on the look than on the reliability.  

As discussed above, the ambient temperature is fairly irrelevant to the temperature within the compartments of your fridge freezer, unless the seals on your appliance are inferior or damaged, as without a tight seal, the warmer air can ingress into the fridge freezer, causing the internal temperature to rise, resulting in the food starting to deteriorate.

It is exactly the same when you look at the insulation provided within your chosen appliance.  In order to bring prices down, manufacturers reduce the amount or quality of insulation.  You should compare the climate class indicated when shopping around, as it is a good indication of how successful your purchase will be. You should also check that the walls of the internal cabinets are nice and thick.

Once you have had your fridge freezer for a while, it is a good idea to check the door seals on a regular basis.  For once, these are very simple to replace and do not cost a great deal.  You just need to ensure you have the correct seal for your make and model.  A good door seal means that the internal temperature of your appliance should remain as static as possible.

Talking of possible faults with your fridge freezer, it is highly unlikely to be caused by a leakage of the refrigerant gas.  It is possible of course that you had a leak when you purchased the appliance, as unless damage has been caused, it is highly improbable this is the cause of a fault.

Control Systems

Depending on the age of your particular appliance, the control system will either be Electro-Mechanical or Electronic.

Electro Magnetic (Old Version):

The system is controlled by a thermostat with a phial that is filled with a gas.  The expanded gas pushes a pressure switch which cuts off the compressor, and once the unit heats up, will switch the compressor back on to control the cooling of the temperature.  A very simple system.

When a thermostat fails, if it is in the closed position, the compressor will run continuously, causing the unit to overfreeze.  If it fails in the open position, it will just not run.

As they come from well-established technology, these systems are very robust  and, therefore, reliable.  The downside, however, is they are not as accurate in controlling the temperature which can vary easily, and can even be 10-15% above the required temperature.

Electronic (New Version):

As noted earlier in this article, these are much more complex.  The unit will use a Printed Circuit Board, which will control run times and check the internal temperature of your appliance by using thermistors.  As the temperature changes, the resistance changes.  This is controlled by the electronic system, and reacts to internal temperatures, keeping them at the required levels.

Although the theory sounds simple in itself, you will know there is a fault when a fault code is displayed on the control board.  This is good as it informs you there is a problem, however, the fault codes are generally incomprehensible!

These control boards are generally on frost free appliances which mean you will have at least three thermistors: one in the fridge, one in the freezer and at least one defrost one to monitor the defrost heater temperature.  On top of this, the defrost heater could also fail.  Any and all of these parts could fail but the fault code displayed on the control board, will not give you the slightest clue as to which part is at fault.

Unless you feel able to investigate further, it is probably the right time to contract a qualified engineer for assistance.  Unfortunately, due to the complexity of the system, it is quite likely that damage can be caused whilst trying to identify the fault if you do not really know what you are doing.  Hence the advice to contact an engineer.

Identifying Faults

As you may now appreciate, it is not always easy to identify the cause of a fault due to the control systems, electronics etc.

However, after a few years hard work, you could possibly have a failed thermistor, electronic control boards or defrost heaters and these are likely to be the root cause of any problem.  The trouble is any and all of the above can throw up all sorts of faults, making it very difficult to know where to start!

There are a couple of things you can check yourself though, before calling an engineer, and may even avoid the need for you to have to go to the expense of having to do this.  For instance, check that the defrost drain at the bottom of the freezer has not been blocked by food debris and frozen over.  Easy enough to clean and remove with a warm cloth.  Minor issue, but if you add it to your normal cleaning routine, it can be avoided.  The other easy to resolve issue is, as mentioned above, check that the door/s are sealing correctly.  This can mean a quick adjustment of the hinges of the door if it is slightly out of alignment, or you may notice the seal is damaged, which can easily be replaced.

If you do decide to carry out repairs youself, please ensure you do not touch anything unless you have disconnected the appliance from the electrical supply.  This advice is even more important when you are proposing working on a large electrical appliance, such as a fridge freezer.










Disclaimer: The information provided has been prepared as a guide only and the steps taken are likely to vary for different appliance models. We strongly recommend using a qualified engineer to undertake major repairs and fault finding.


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