Fridge Freezer Repair Help Guides
Frost Free Fridges And Fridge Freezers
- Created: Sunday, 06 November 2005 14:56
- Last Updated: Tuesday, 19 July 2016 14:40
- Hits: 63111
How Frost Free Fridges Work
Seems like a great idea, freezers that never need defrosting due to the fact that the frost doesn't build up in the first place and it is a great idea too but, there is no doubt about it, frost free causes a lot of problems that are not easily sorted.
In a normal freezer, the evaporator i.e. the parts on which the frost forms is exposed, these are the pipes you can see that often actually form the shelves. The frost builds up on these and, if left, will completely take over the space where you should be able to place your food. When defrosted, usually just by switching the appliance off, the ice melts and drips all over the base of the freezer hence the need for towels etc. In a frost free appliance, the cooling evaporator is concealed, often behind the cover at the back of the inside of the freezer or in a compartment at the top. The evaporator is formed of pipes, similar to a normal freezer, but with fins attached. An electric fan draws air from the cavity (i.e. the food stored inside), through the finned evaporator and then back into the cavity again for the process to continue. Frost will therefore still build up on the evaporator but, due to its compact nature, it can be carefully monitored and defrosted by a small heater with the water running neatly down a drainage hole onto a tray mounted above the compressor from where it will evaporate. If the appliance is a fridge freezer then the fridge compartment may have no working parts in it at all, refrigeration will take place by simply opening a mechanical flap from the freezer which will close once the temperature is correct.
Do not confuse frost free with auto defrost fridges, they are completely different.
Although the video above is a promotional item for Fisher & Paykel's "Active Smart" refrigeration range it does offer a lot of insight into the general workings of a frost free fridge freezer.
Parts Of A Frost Free Fridge Freezer
As well as the normal refrigeration system, i.e. a compressor, evaporator and condenser, frost free appliances will have a number of special features with which to control the defrosting.
As mentioned above, most will have a fan which may be visible from inside the freezer and will be heard running. If your fan is not running, don't automatically assume it is faulty as they may switch off when the door is opened and when the correct temperature is reached. In general, evaporator fans don't cause a lot of problems and rarely fail although often they become noisier than they should be and are changed for that reason.
Freezer Defrost Heaters
The defrost heater will be wrapped around the evaporator and melts the ice build up when energised. Another heater will be placed around the drain hole where the defrosted ice water will run through, without this heater the drain will freeze over and become blocked. These may be protected by a thermal fuse which cuts the circuit should the heater become to hot.
Fridge Freezer Temperature Sensors
These usually are thermistors, resistors that change their resistance value with temperature changes. These are usually located on the evaporator and another one somewhere inside the freezer cavity. In the case of fridge freezers, there will also be another one within the fridge. These all feed information back to the controller which will react accordingly. I.e., switching on or off the compressor and fan as necessary to maintain the correct temperature.
Fridge Freezer Control Module
This is the main controller, nowadays an electronic PCB, often with a user display showing actual and set temperature. This controller will collect and compare information from the thermistors and activate the necessary action. It will also control the defrost programme. Some more basic, earlier frost free appliances use a mechanical thermostat and timer rather than an electronic version.
Automatic Fridge And Freezer Defrosting: How It Works
Most frost free freezers are usually defrosted after a set time period. In the case of Hotpoint Mistral types, this is every 10 hours. The defrost heaters are turned on and will remain on until the thermistors record a temperature of, in Hotpoint's case 20°C at which point the evaporator heater is turned off while the drain heater remains on for a further 5 minutes to allow for all the water to drain off. The compressor will then start and once the evaporator thermistor is reading -5°C the fan will re start.
What Goes Wrong?
With all these electronic devices there is a lot that can fail. Diagnosing is not easy as any engineer will testify.
The most common problem is insufficient cooling, often in the fridge first before the freezer itself warming up. This is usually due to the build up of ice on the evaporator not being defrosted and building up to such an extent that the air passage through the fins, so vital to the fan action, is completely blocked. Manually defrosting will restore normal use but, unless the cause is rectified, the fault will return, in time. In general, the biggest problem we find is with the thermistors themselves giving false or no information to the controller. Not possible to test but usually relatively cheap to replace as a first try, although some may be foamed in to the actual insulation of the appliance and, in some cases, are non replaceable. Defrost heaters can also fail, but not so common these days and can be checked for continuity and earth faults with a test meter. As stated above, these are often protected by thermal fuses which are more likely to fail and again can be easily tested. If failed though, they may indicate another fault that may have caused overheating.
The control module itself is often the cause of problems, either missing defrosts or not re starting after defrosts are common faults. Not possible to test without replacement which may be costly.
Fridges And Freezers Need Adequate Ventilation
Nearly all frost free appliances require a healthy air flow to operate correctly. Ensure that the appliance is not installed in a sealed unit unless it is designed to be and make sure any vents are not blocked.
To sum up, frost free is not simple to either work on or diagnose faults and once defrosted, the fault may not show up again for a long period. We would advise expert attention where possible. If you do look yourself, make safety your number one concern. All circuits are 230v mains and, coupled to the likelihood of water being around can and will kill you! So make sure its all unplugged before removing any panel. Also watch out for the fins on the evaporators as they are RAZOR sharp. Do not attempt to defrost with any tool as puncturing the system will wreck your freezer. Do not be alarmed if your appliance does not start up immediately when turned on. This may be timed to protect the compressor and may take up to 30 minutes before starting.
Fridge not cooling but freezer coldMy fridge is not working but the freezer is , I was told (though its frost free) to switch it off for two days and it might just work by itself , if didn\'t call out for service . Has this worked for anyone
I also think its too close the wall and might be clocking the air (as it is free standing)
Any ideas ?
Fridge freezerI have a Fisher Paykel fridge freezer. (freezer below fridge). The fridge compartment has suddenly started to freeze food. I have tried various temperature settings without solving the problem. The fridge is about 17 years of age ( too old?) . Can you help? Regards Frank
Hot point FF not workingI have a Hotpoint fridge freezer (FFA97P) which has stopped working.
I can hear the fluid bubbling at the rear of the unit but it does not appear to be circulating around the cooling pipes inside the rear cowling where the fan is located.
The fan is not working either.
I have replaced the Capacitor but that has not made any difference.
Any advice welcome.
Liebherr Freezer problemI have a Liebherr stand alone stainless steel freezer, model number 7080 393. I\'ve had this for a good few years and it hasn\'t ever given me any problems until recently.
Over the last weeks I\'ve had water on the floor of the kitchen. The freezer seems to be working OK and I have defrosted it some 2/3 days ago. At the back of the freezer there\'s a plate behind the compressor where water condenses and then drops onto the floor. Can someone give me some idea what the problem may be and if I need to buy a replacement part. Thank you.
To be honest you would be better to ask in the forums but you will need to get the service number so that anyone can look the machine up for you.