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. 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.

  2. 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

  3. 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.

  4. 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

  5. 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.

  6. The fridge Man

    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

  7. 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.

  8. 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.

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