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Blog > Fridge & Freezer > Frost free freezers and automatic defrosting fridges, how do they work?

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 heater 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. 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

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.

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.

Written By - Washerhelp on June 8th, 2009 with 43 comments
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43 Comments

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Philippa Philippa
#1. July 6th, 2009, at 4:05 PM.


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

Washerhelp Washerhelp
#2. July 8th, 2009, at 2:19 PM.


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 SKB
#3. July 18th, 2009, at 12:41 PM.


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 Vince
#4. August 25th, 2009, at 5:34 PM.


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.

Washerhelp Washerhelp
#5. August 28th, 2009, at 5:28 PM.


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
#6. January 3rd, 2010, at 3:45 PM.


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

Washerhelp Washerhelp
#7. January 7th, 2010, at 1:15 PM.


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 mike
#8. January 17th, 2010, at 8:08 PM.


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 Washerhelp
#9. January 18th, 2010, at 11:23 AM.


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 ernie
#10. January 23rd, 2010, at 4:54 AM.


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???

Washerhelp Washerhelp
#11. January 24th, 2010, at 2:12 PM.


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

GEORGE GEORGE
#12. February 22nd, 2010, at 11:43 AM.


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

Washerhelp Washerhelp
#13. February 23rd, 2010, at 11:42 AM.


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.

GEORGE GEORGE
#14. February 25th, 2010, at 9:59 AM.


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 ?

Washerhelp Washerhelp
#15. February 25th, 2010, at 5:36 PM.


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.

pat clarke pat clarke
#16. March 5th, 2010, at 7:53 AM.


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

Washerhelp Washerhelp
#17. March 6th, 2010, at 3:03 AM.


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.

gerry walker gerry walker
#18. March 30th, 2010, at 6:45 PM.


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

Washerhelp Washerhelp
#19. March 31st, 2010, at 3:24 PM.


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

emma emma
#20. April 2nd, 2010, at 2:03 PM.


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?

Washerhelp Washerhelp
#21. April 4th, 2010, at 4:45 PM.


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

farro farro
#22. June 28th, 2010, at 4:48 PM.


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.

Patricia Patricia
#23. June 29th, 2010, at 8:56 PM.


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

Washerhelp Washerhelp
#24. June 30th, 2010, at 2:27 PM.


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.

Patricia Patricia
#25. July 1st, 2010, at 2:00 PM.


Thank you for your reply, it is appreciated

mr drame mr drame
#26. July 4th, 2010, at 12:43 AM.


can you tell me please wich parts of the frost free fridge usely got probleme ,defrost heater ,defrost timer,thermostat,or the sensors.and how do i know that 1 is not doing his job proply by using an electrical tester.thanks

Washerhelp Washerhelp
#27. July 5th, 2010, at 2:39 PM.


Frost free fridges have a lot more parts to go wrong such as the ones you mention but remain one of the more reliable appliances we have. I don’t think you can test sensors very easily. Engineers usually just replace them if they are suspect or if an error code implicates them.

The fridge Man The fridge Man
#28. July 8th, 2010, at 10:49 PM.


mr dame to check sensor using a multimeter you should get a reading between 6 and 27 kOhms depend on room temp higher reading at colder temperature.
Defrost heater should have resistance of about 300 ohms
Drain heater should be about 1000 ohm (heater resistance depending on model and heater wattage)
thermal fuse should be very low resistance usualy about 1 to 3 ohms.
Looking for ice biuld up can tell what problem is
if ice is very white and fluffy looking at top or bottom of evaporator usually air flow problem.
if it’s clear and very solid looking prob drainage problem
if evaporator is completly covered usually defrost problem

Washerhelp Washerhelp
#29. July 9th, 2010, at 10:21 AM.


Thanks fridge man. I didn’t have the exact resistance readings and the question was pretty general covering lots of parts. Thanks for taking the trouble to put some figures up.

Washerhelp Washerhelp
#30. July 10th, 2010, at 11:07 AM.


The fridgman: Further to my reply, as far as I’m aware most engineers don’t test sensors as if they are faulty they should cause an error code in most modern fridges. Most engineers these days go on error codes, if an error code says a sensor is faulty they will just replace the sensor and not test it, especially as it involves stripping down to test. They will just order a new sensor and replace it.

Unfortunately the good old days when an engineer determined a fault using skill, experience and a test meter are just about finished – especially with regards to engineers working for large repair companies and even manufacturers. Most of these engineers operate by ordering lots of parts and hoping it will cure the fault.

DIYer DIYer
#31. August 1st, 2010, at 12:14 PM.


My problem started when we discovered that we could not close the freezer door. This was because the back panel had been pushed forward (by ice behind it, as it turned out), forcing the food drawers forward.
I took off the back panel (next time I have to do this I will turn off the freezer for a couple of hours to prevent ice sticking to the back of the panel and damaging the foam insulation). On removing the panel I discovered that the bottom half of the evaporator was solid with ice, the top half completely free of ice/frost.
It took ages to melt this ice, even using warm air from a hair dryer. After a while, the water drain came into view, and the melting water went down it, no problem. There had been nothing blocking this drain, apart from ice! When all the ice had melted, I replaced the back panel (with restored foam insulation) and everything is now perfect – apparently – time will tell.

But, how did the drain get blocked with ice in the first place?

Now, my freezer (a Hotpoint FZA80) has a ‘fast freeze’ button. I guess this cuts out the defrost cycle when it is used – and this means that when the freezer returns to normal operation the first defrost cycle will melt a lot of ice, perhaps with chunks falling off and blocking the drain hole. What say you? Should I advise my wife to stop using the fast freeze button?

Washerhelp Washerhelp
#32. August 2nd, 2010, at 3:08 PM.


Hello DIYer: I would have thought using fast freeze should only freeze up the hole if it’s already blocked and already full of water. Otherwise it shouldn’t cause any problem.

Frost free refrigeration relies on the defrost cycle warming up the ice and having it run down the back wall and collect in the runners that channel it to the hole in the centre. From there it runs out to a tray on the main compressor (which gets naturally hot) and evaporates. Frost free freezers can suffer from the hole getting blocked up which can cause future water to run into the base of the fridge instead and freeze up.

Kirsty Kirsty
#33. August 13th, 2010, at 8:09 PM.


Our top of the range AEG frost free freezer is almost 3 years old. We never take out those extended warrantees so it is not covered. It has had a mind of its own recently, with its alarm going off, its temp varying between minus 10 and minus 20 despite being set at minus 18 and finally I called the number on the instruction book. Was advised to take out a year’s extra cover for £160 and the engineer came today. Had already parked the surviving food with neighbours and had a clear-out of the dross. Needless to say, once empty it was behaving perfectly. The engineer said ‘frost free’ does NOT mean don’t defrost. He showed me the frost buildup behind the grill at the top of the fridge. He advised me to turn it off for 24 hrs, clean it out (it looks perfectly clean) and restart. He practically guaranteed that it would be ok. Why on earth don’t they mention any of this in the manual? I am going to have a go at AEG but no doubt will be fobbed off. We are two adults who use the freezer and we do not leave it open for long. I am furious that such a simple remedy has cost me £160 – I could have paid a call out fee of £70 plus VAT but didn’t quite dare go for this option in case it goes beserk again. Will keep you informed, but be warned and do defrost your frost-free about annually. What a bore.!

DIYer DIYer
#34. August 14th, 2010, at 11:27 PM.


Defrosting a frost free freezer. Beware a flood. If it’s like mine, there is nowhere for the melted ice to go until the hole mentioned by Washerman is free of ice or of any other blockage, therefore until this hole is free it will overflow and end up on the floor! and even when the hole eventually becomes clear, the melt water will go to the tray over the compressor, fill it, possibly overflow and cause more agony.
Defrosting takes a long time – have your mop ready.

Washerhelp Washerhelp
#35. August 17th, 2010, at 4:24 PM.


Kirsty: Frost free does mean you shouldn’t have to defrost, if it’s not mentioned in the manual that proves it. If a fault develops, ice can form, or it can form if the door is left open accidentally in which case you would need to defrost it but in normal operation it shouldn’t create any ice.

Unfortunately with frost free freezers the ice forms out of sight so you aren’t aware it’s there but whilst ever it is the freezer wont function properly. They also take a long time to defrost for the same reason, the ice is packed around the fan or evaporator which is being insulated panels. A minimum of 12 hours defrosting is needed and possible even longer depending on ambient temperatures.

Washerhelp Washerhelp
#36. August 17th, 2010, at 4:25 PM.


DIYer: I would also enlist the use of some large towels.

DIYer DIYer
#37. August 21st, 2010, at 12:27 PM.


Washerhelp. See #31 and #32. Due to the construction of my freezer there is absolutely no way the the drain hole can be blocked by anything other than ice – so the origin of my problem is still a mystery. (My actions under #31 seems to have succeeded). I can only assume we left the door open inadvertantly for a lengthy period. Even so, with no foreign matter blocking the hole, I can only assume that a chunk of ice fell off the evaporator during the defrost cycle and lodged in the drain.
Maybe it depends on which direction the fan blows!. I would like to think it draws cold air from the evaporator and blows it over the food trays and not the other way round. (I’m suspicious since my manual says that the lower trays are the best ones for getting a faster freezing rate, suggesting that the fan pushes air past the evaporator so that the emerging cold air hits the lower trays before the upper ones – the snag with this is that the air would encounter the drain hole almost immediately after passing the evaporator.) Either way, some of this cold air must go down the drain hole so that if there is a parial blockage due to a fallen lump of ice, then this current of cold air may make the blockage complete.

Many thanks for your excellent site – without it I feel sure that like Kirsty, (#33) I too would have been stung for £160 or so. Thank you.

Washerhelp Washerhelp
#38. August 24th, 2010, at 3:30 PM.


DIYer: Thanks. The lower trays should be colder because of the cold air being heavier and congregating more at the bottom, just as in an oven where conversely the hottest air is at the top.

Carol Carol
#39. August 27th, 2010, at 6:46 PM.


Hi, can you advise please, I have a Bekko frost free fridge freezer, only 6 weeks old which makes an awful whining noise, getting higher and higher and then suddenly stops. The motor seems to come on every 20 minutes or so for about 8 to 10 minutes although I only have the thermostat set at number 1. Is all this normal.
Thankyou.

DIYer DIYer
#40. August 28th, 2010, at 1:08 AM.


Carol. Can’t really help you with this. More details needed. Does the freezer actually deliver the goods – that is, does it freeze your food at the right temperarure. If not then I suggest you get on to your supplier, otherwise, how noisy is it? maybe the compressor is noisy when it is active. There is no whining noise from my freezer, whatever it is doing. I think you should raise this with your supplier, presumably your freezer, six weeks old, is still within warranty. I feel sure Washerhelp would agree. If they fob you off (as Phillips did with me over a DVD player) fill out a small claims court action. Phillips succummed immediately despite their prior adamant denial of any responsibility.

Washerhelp Washerhelp
#41. August 31st, 2010, at 12:17 PM.


Carol: The noise could be the fan catching on ice, especially if it’s a high pitched sound, which eventually stops dead. You could try a 24 hour defrost leaving door open, but if it cured it and the noise returned or if it didn’t make any difference you’d need an engineer to look at it. ( Appliance Repairs)

sharon ellsworth sharon ellsworth
#42. September 2nd, 2010, at 12:42 AM.


hello, my 15-yr.old GE fridge [the label says "no frost"] was not freezing anything in the freezer & the icemaker was not working. a repairman came out & said it needed a new “defrosting system” [later he said it was a new thermostat]. he said to unplug it for about 24 hr. & he came back & fixed it. that was about 4 days ago. it seemed to be working but then today i noticed some frost accumulating again on the back wall of the freezer . . is some frost normal? should i call the repairman back out? Help! thanks!

Washerhelp Washerhelp
#43. September 2nd, 2010, at 11:36 AM.


Sharon: If it’s 15 years old it may be different to modern freezers. If you have the instruction book see what it says. If it has automatic defrosting on the freezer it may be normal.

With automatic defrosts the back wall should get a covering of small globules of ice or frost, which when the defrost cycle takes place turn to water, run down the back wall into the v shaped channel at the bottom and run out through to the evaporation tray on top of the compressor.

Alternatively if the door seal is letting air into the freezer it could cause moist air to be constantly drawn in which will turn to frost (as mentioned in the main article).

 

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