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

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.

Whilst we are on with American style frost free fridge freezer’s, because the door’s 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 seal’s regularly.

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. This tray sits on top of the compressor and gets quite hot. The water simply evaporates. Sometimes this hole gets clogged up and prevents the water running out to this tray. The result is that water runs into be base of the unit. Very often the appliance will come with small tool for cleaning out this hole, but if not you can improvise.

If the water in the base of the unit is frozen solid it could be that the unit has malfunctioned and is over freezing. The blockage preventing the water running through to the evaporator tray could actually be solid ice.

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.

Instruction manuals 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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Comments

  1. avatar Philippa says:

    I am puzzled as to why, in many modern fridge freezers, only the fridge is frost-free?

  2. The freezers are frost free and accomplish this by hiding the evaporator behind the plastic wall and blowing the cold air around the freezer compartment using a fan.

    Fridges shouldn’t normally attract frost as they don’t get cold enough.

    Modern refrigeration automatically defrosts using a timer and a heating element which raises the temperature just enough to melt any ice and letting it run down the back wall to the back of the appliance where it evaporates.

  3. What a well written article. Thank you for taking the time to do so. We are having just this problem and will try a full 23hr deforst before buying a new unit as we thought we wouyld have to.

  4. Below is the exact same problem I am having. What causes this?

    Thanks for the help, Vince

    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. This tray sits on top of the compressor and gets quite hot. The water simply evaporates. Sometimes this hole gets clogged up and prevents the water running out to this tray. The result is that water runs into be base of the unit. Very often the appliance will come with small tool for cleaning out this hole, but if not you can improvise.

    If the water in the base of the unit is frozen solid it could be that the unit has malfunctioned and is over freezing. The blockage preventing the water running through to the evaporator tray could actually be solid ice.

  5. Vince: It could be a sensor fault or even a pcb fault, or something else. Best get someone to look at it as they can be tricky to diagnose.

  6. avatar Anonymous says:

    is there any difference between “FROSTFREE” and “AUTOMATIC DEFROST”?

  7. Hello Anonymous. Automatically defrosting wouldn’t necessarily mean an appliance is “frost free”. My understanding is that frost free refrigeration operates by blowing cold air into the compartment instead of having an exposed condenser cooling the air.

    An appliance could be a normal unit that just has an automatic defrost which negates the need to manually defrost it, but frost could still accumulate prior to the defrosting operating.

  8. Thanks for casting more light into this dark area. From my research it seems that Americans use the terms auto-defrost and frost free interchangably, as if they mean and are the same thing. Obviously they are not. But see the quote from Comet below.

    I only learned today from a guy at Currys that auto-defrost only applies to the fridge (and most new ones are, even if they don’t say so). This is the auto defrost described in the above article.

    Comet “helpfully” answered the question this way:

    Auto-defrost – this automatically regulates the temperature in your fridge to prevent frost build up. Frost Free models mean there is no build of frost and would not require de-frosting.

    That should be clear to everybody!

    What I am trying to decide is which to buy. Frost- free means: costs more to run (I have seen 20% quoted), more expensive to buy, less room for food, and more technology to go wrong. Plus, the regular warming cycles can be detrimental to the food and reduces its storage life. Are all these factors really worth having?

  9. Mike: The name auto defrost implies there must be some frost to de-frost, therefore any appliance with auto defrost can’t be frost free or there’d be nothing to defrost. These appliances work “normally” but have a heater and a timer built in, which automatically defrosts it by warming up the appliance inside and causing the water created to run down a channel at the back. From there it runs out onto a tray mounted on top of the compressor, which runs hot enough to evaporate it.

    Frost free means it doesn’t create any frost and this is achieved by hiding the evaporator behind the back wall and circulating the cold air created by it over the food. It usually refers to freezer compartments which used to gather thick layers of frost.

    As you point out there are several disadvantages to this including extra cost, more parts to fail, less storage space and less storage life. Each time an extra convenience is created it’s usually at the cost of compromise elsewhere but we rarely get informed of the pros and cons and rarely get a chance to choose, they just steam ahead and decide that’s what everyone would prefer.

  10. Our Prestige fridge freezer (frost free) makes a noise like jack hammer) and then goes quiet. we haave been told by COMET that this is normal of frost free fridge freezers? is this normal?

  11. Hello Ernie, yes they can make some very loud cracks as the back wall releases from the evaporator during defrosting.

  12. 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

  13. Hello George. Thanks, any decent frost-free fridge freezer should have a separate sensor for fridge and freezer. But as my article Freezer defrosted: Can you put a fridge freezer in a garage? describes some (presumably budget brands) only have one sensor or thermostat in the fridge section which causes problems if the unit is placed in a colder than a normal kitchen environment.

  14. 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 ?

  15. 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.

  16. avatar pat clarke says:

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

  17. 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.

  18. avatar gerry walker says:

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

  19. Gerry, it might not be perfect but I wouldn’t have thought it would be a problem.

  20. 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?

  21. Emma: The gasses pumping round can make gurgling and strange noises.

  22. I am wondering if the fan in the freezer on a frost free appliance is always on or does it switch on and off. The fan in my frost free has stopped working i think and i am finding that sum of my food is not freezing. I have noticed this has happened since my daughter left the freezer door open and it was a good few hours before i noticed. Could this have affected the running of it?. I have had the appliance over 5 years. I have read on the internet that it could have frozen up due to the door being left open and to unplug it and defrost it completely.

  23. avatar Patricia says:

    As a disabled person would I find it easy to defrost an upright freezer? Our frost free has proved unreliable and we need to replace

  24. Farro: The fan should switch on and off to maintain the right temperature. If it’s stopped working after the door was left open it may have iced up around it. This would normally be preceded by some strange noises as the fan started catching on the ice before it finally stopped. If possible you should try totally defrosting the appliance for a full 24 hours. That packed ice is hard to get rid of so any less wouldn’t work.

    Patricia: It should be easy to defrost an upright freezer, the water should run just down into a bowl at the bottom.

  25. avatar Patricia says:

    Thank you for your reply, it is appreciated

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