Frost free freezers and automatic defrosting fridges, 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
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 below..)
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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Philippa says
I am puzzled as to why, in many modern fridge freezers, only the fridge is frost-free?
Washerhelp says
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.
SKB says
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.
Vince says
Below is the exact same problem I am having. What causes this?
Thanks for the help, Vince
Washerhelp says
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.
Anonymous says
is there any difference between “FROSTFREE” and “AUTOMATIC DEFROST”?
Washerhelp says
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.
mike says
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?
Washerhelp says
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.
ernie says
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?