It is all to do with the surface tension of water.
The design of the fridge is basically a fan to blow the fridge air over a finned cooling heat exchanger set vertically down the centre back of the fridge. The cooled air then comes out at various points down the fridge to maintain an even cold temperature.
After a time, the fridege goes into defrost mode to melt the ice build up on the heat excanger and under gravity the water runs down and out of a drain pipe located directly below the heat exchanger. So far so good
Unfortunately, in order to get good air cooling the heat exchanger has lots of fins closely packed together set along the vertical coolant pipe. (The fin spacing is only 2 to 3 mm.) Therefore the fins are not very far from horizontal and very close together. This means that although the ice melts the water does not completely run off from between the fins. A small quantity is held by surface tension along the bottom space between successive fins when the defrost cycle finishes.
This water refreezes and is of sufficient quantity not to melt in the next defrost cycle. Indeed each cycle causes a little more ice to build up. The fridge therefore works for some months without a problem but eventually the heat exchanger becomes a solid block of ice touching the plastic cover plates whereupon ice starts to form on the front of it.
Removing the ice from this section will not cure the problem. You need to remove the plastic cover sections to gain access to the heat exchanger behind them and pour boiling water over it until all the ice (AND WATER) is removed from between the fins. In total it took me several hours.
Remove a narrow plastic strip at the top using a small screwdriver in one of the small holes. Then remove the screws to take off the top cover section. Pull towards you on the left. You may find it difficult because the ice build up prevents getting the plastic plate out on the right hand edge. Do not force it and be patient. I did not have any, but windscreen de icer sprayed behind the plastic, especially on the right hand side will help speed up the melting. A hair drier set to warm not hot will help to remove all the moisture at the end.
As soon as ice starts to show on the front of the plastic panels the job will need to be repeated. However if you have removed all the ice and dried it it should last as long as it did from new.
Dr Michael S Short
May 2007