How do they work?
Frost free fridge freezers are very popular and auto defrosting fridges are a great convenience. In a frost free appliance the cold air is blown round the freezer using a fan. On modern refrigeration the evaporator (which is the plate that gets cold) is hidden behind the plastic wall inside at the back of the food shelves. When working correctly you can usually see small beads of ice randomly scattered on the back wall unless it’s in a defrost cycle when you may see water.
Heater inside
the 
Believe it or not most modern refrigeration has a heating element inside. This heater is used to defrost the appliance automatically. During the defrosting cycle the ice on the back wall melts and runs down the back wall into a channel. It is then directed through a hole out through to the back and runs into the evaporator tray. The evaporator tray is on top of the compressor which gets pretty hot and evaporates this water into the air.
Because the evaporator is behind a back panel the cold air has to be blown around the compartment with a fan motor. The defrost cycle also needs sensors and a timer and combined with several sensors throughout and PCBs to control everything the result is there is a lot more to go wrong than there used to be in old-fashioned conventional fridges. However, they are still fairly reliable.
Common problems with frost free fridge freezers
If the door is left open for too long (especially in humid conditions) the evaporator freezes over and the unit will not keep the food cold. This problem (unlike the older machines) has a greater impact because you can’t see the amount of ice built up around the back of the panel hiding the evaporator.
In many frost free fridges the ice can form all the way round the fan and cause it to run slowly or even seize up. Prior to seizing up the fan may catch on the ice and make a high pitched noise. This will of course result in the fridge or freezer not getting cold. If you hear a strange noise from your frost free fridge freezer which sounds like something is catching on a rotating fan it could be due to ice forming around it.
If it stops working due to ice forming behind the evaporator and round the fan then defrosting the unit manually can fix it but it involves unplugging the unit for at least take 12 hours or so.
You may not see much frost as it would be behind the back wall or behind the fan unit.
You can’t really use a hair dryer on modern units because they may have a thermal fuse which protects the defrost cycle.
Also, even just getting to the evaporator to defrost it can be a mammoth task especially with some of the new American-style fridges.
If a fault re-occurs later it could be due to faulty sensor but if the fault was only due to the door been left open for a few hours accidentally then a total defrost could work. This demonstrates the type of problem many people have when confronted with these larger bulky hoses with specific fitting instructions as described in the main article on the left.
Water or sheet of ice inside fridge
If your fridge has two sloping channels at the back wall and a hole in the middle this is designed to channel the water created on the defrost cycle through to the back of the unit where it runs onto an evaporator tray which can get blocked. More details on this here- Ice or water in base of fridge or freezer.
Whilst we are on with American style frost free fridge freezers, because the doors are so big and can store so much, the opportunity to overload them is greater. This too causes warm air to pass into the unit and frost it up.
Remember a frost free unit will not cope with too much ice on the evaporator so greater care must be taken to use it correctly and check the door seals regularly.
Summary
It’s common knowledge that most people rarely read the instruction book supplied with their new appliance. This is particularly true with something like a fridge or freezer. It’s easy to imagine most people thinking you only need to plug it in, leave it plugged in, and fill it with food – what’s to know?
I would advise anyone with a modern refrigeration appliance, especially the American-style fridge freezers, to carefully read the instruction book. Modern frost-free refrigeration units work very differently to a conventional fridge or freezer. It’s even important to learn how to stack them properly otherwise you can prevent the air from circulating inside and cause warm spots.
You would be surprised at what you can learn from reading the instruction book of an appliance you already know how to use. Many User instruction manuals can be downloaded here.The page concentrates on washing machine manuals but links to appliance manufacturer sites where users such manuals for fridges, freezers and other appliances should also be available.
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Firstly thanks for all the great advice on here! We just got our new AEG frost free fridge-freezer today, and was concerned about the the noises it’s been making since switching it on – I can only describe it as strange scraping-like sounds that vary in noise level. Is this a normal noise?
The other thing I’m a bit worried about: it’s supposed to have a charcoal air filter in the fridge, but never came with one. Is it essential to have one of these or is it ok to operate without one? Thanks for your help!
Hi Sylvia: Thanks very much. You can get lots of strange noises from modern fridges including whooshing noises, the sound of something liquid running through pipes and even the occasional loud cracking sound. Obviously any noise that suddenly starts and continues may be cause for concern but when new you don’t know what it should sound like. I can only advise to see if it settles down and use your judgement as if it sounds like something is wrong or not.
A charcoal filter would only be to help reduce food smells. It might be useful but not essential.
Hi, I’ve noticed that on the back of the inside of the fridge of my 4.5 year old Miele fridge/freezer has iced up considerably and I hear the occasional loud knocking noise coming from it. Any ideas what this could be? Shall I try and defrost just the fridge and see if it comes back? Thanks!
I just got a new Frigidare frost free freezer/upright. The sides are hot to the touch; I also wondered…I can hear the fan running constantly. Is this normal? Thank you
I would try a defrost Tony R.
Jenny: Check your instruction book, hopefully they will mention these things. Frost free fridges can get hot at the sides and the fans do run on and off a lot but shouldn’t run constantly once settled in.
Washerhelp,
Just found your site. What a help I found it. My sanity is returing.
Situation: Am really rather ill. Have to store temperature controlled drugs injections in fridge 2 – 8 degrees. It’s a relatively new, expensive fridge/freezer. Jabs are useless if go out of temp. – it’s a nightmare. This stuff can cause cancer and lupus, etc.
Got a data logger. Seems the unit is suceptible to room temperature of kitchen vv cooking, food retrieval, overnight drop in the air temperature. I live in a bungalow. data logger shows teemp. in fridge drops to 1.5 during the night.
There must be millions of people who are storing vital drugs in domestic fridges and have no way of knowing that they have ‘gon out of temperature’. I have tried to engage the press media over here to address the situation as I feel the responsibility, loaded by the NHS, on folk who are already very ill is unacceptable. Sadly, they don’t recognise the importance. I have seen that the US authorities have seen the situation and are currently researching dedicated units – pity UK authorities are turning a blind eye.
I’m now going to buy a pharmacy fridge and hope that this will resolve the problem. I’m undecided whether to call an engineer to look at this Bosch fridge/feezer I have, or to cause it’s demise with a 15lb hammer! There must be a problem because the frequent fall of ice into the tray is sufficient to wake one up – from the other end of the house.
If you’ve read this … thanks for your patience. this morning I need to rant – I’ve been up since the crack of dawn.
Rgds Jean
Hello Jean UK: You are right in that you may need a pharmacy fridge. No domestic appliance manufacturer is going to guarantee their refrigeration is suitable for looking after such delicate medical products. Normal fridge temperatures should be between 0 degrees and 5 degrees so 1.5 degrees is perfectly OK for normal use.
The coldest part of a fridge is usually at the bottom, have you tried monitoring the temperature at the bottom of the fridge in case it remains colder? Also I would try setting the temperature as low as you can without getting lumps of ice in the milk, that could make a difference too.
Hello Washerhelp,
Sorry for the delay in answering. Been experimenting. Nope! Nothing works. Have now got a pharmacy fridge, all checked, set up and doing the business. I was abolutely amazed at the service/delivery … ordered it one day, here before 1pm the following day.
I can now sleep at night and stop asking questions which must seem daft to those in the trade. Thanks for taking the trouble to ‘hold my hand’ – I was glad of your input. Take care, and may all your problems be small and solvable.
Hello,
I bought a new frost free fridge freezer and the fridge started to develop a very tiny ice layer at the inner back panel which is defrosting every hour or so. The problem is the fridge is constantly wet and even the glass shelves are sweaty. An engineer came and said it’s normal, however I’m concerned so please help!
Tanya: It’s normal for the back wall to ice up and defrost regularly but not in a sheet, it normally has many globules of frosted ice. It might for a so-called sheet but it shouldn’t be a smooth sheet of ice, just a covering of small drops of water that have frozen.