Frost free freezers and automatic defrosting fridges

How do they work?

Fridge Freezer 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 Heater 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

Ice 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.


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.

Instruction manuals 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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118 thoughts on “Frost free freezers and automatic defrosting fridges”

  1. jeremy: Water should run down into the evaporator tray after being defrosted by the heat from the defrost heater, which literally melts the ice. It should run into the tray on top of the compressor at the back of the machine. From there it is supposed to evaporate using the heat generated by the running compressor. If it’s not evaporating I wonder if for some reason the compressor isn’t running hot enough?

  2. I’m looking for a american fridge freezer from comet for £600 or less. When comparing products all of them say Frost free but only one of them says automatic fridge defrost. But like you I thought if there’s no frost then why would you defrost it. So should I just ignore this feature.In your opinion what’s the most important feature to consider and compare when buying a new Fridge Freezer ?
    Thank You

  3. Zac: Yes a fridge only goes down to about 5 degrees so there should be no frost, but modern fridges can get excessive ice build-up on the back wall. They have an evaporator at the back wall which gets very cold and forms drops of ice, the cold is pumped round the fridge by a fan and every so often they defrost. The water runs down a channel out of the back of the fridge.

    I would recommend taking advantage of the Which? 30 day trial which gives a great deal of genuine resources to research for only £1 and then spend some time researching their refrigeration reviews, advice and best buys in the fridge freezer section Which? Special Offer details

  4. keith mcknight

    Defrosted Hoover frost free with hot air gun. BIG MISTAKE Now it won’t switch on?

  5. Keith: A hair dryer is often used by engineers although it takes so long even with a hair dryer none would have time to do it except in particular circumstances. Best method is a full 24 hour shut off with doors open and lots of towels to catch defrosted water. A hot air gun such as one used for paint stripping would definitely risk damaging something.

  6. Hi, I’ve got a beko 50/50 fridge freezer – frost free, 9 years old, only one stat, fan in freezer constantly going along with compressor, but fridge not very cold …well warm really..but does get beads of water on back wall..but not cold enough to chill a 4 pack. Used to be excellent but now even on highest setting it’s no good any advise would be greatfully received.

    Freezer is working fine and its below the fridge

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