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. Your article on ‘how does it work’ is very helpful but could you please explain the exact sequence of events from initial switch-on of a frostfree fridge freezer. e.g. what determines the temperature of the freezer section as I understand that the variable stat only controls the temperature in the fridge section. Maybe a little circuit diagram or would that be too much to ask. thank you

  2. Thanks washerhelp, I had thought that there would have been a second (hidden) thermostat controlling the freezer section. I guess I have the economy version, from Comet. Very hard frost coupled with a heating problem may have been the cause of my problem as the offending article now seems to be working again albeit with a wild temperature swing in the freezer section, from -8 to -30 , would that be normal ?

  3. I would say that if you have the ability to set the temperature for the fridge and the freezer separately then there should be two separate sensors for that to be possible. A sensor in the freezer is not likely to be visible and behind the panel at the back.

    If you have a fridge freezer with just one temperature control that you can adjust warmer or colder it may just have the one sensor controlling the fridge and freezer.

    The temperature inside the freezer should normally be -18 degrees.

  4. Can a frost free freezer be housed in a confined space or should there be gaps between the walls and the freezer?

  5. As with most appliances air needs to circulate around the appliance. Some modern fridges can get quite hot on the sides so ideally they need to be able to cool off. The main requirement would be space at the back where the compressor is for air to circulate.

  6. I have tiny kitchen and fancy a fridge freezer. The only location would be a foot from the cooker. Is this too close?

  7. Hi, Our self defrosting ff is making a funny noise. It started last night – more of a shrieking noise rather than the loud cracking sound we usually have encountered. I can also hear water going around it – is this normal?
    I have tried plunging the hole in the fridge and have made sure the fan in the freezer is clear of food. The freezer has now started to defrost but not sure if this is the sekf defrost or wether it is not working properly?

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