Samsung RS21FCNS

We’ve had the Samsung RS21FCNS American style FF for the last 2 1/2 years. As FF’s go it has been very good.
However, it seems that we are suffering from a problem that many others seem to have – the evaporator keeps icing up.
I, like many others it would seem, have searched the net for possible answers. I again like others have come to the conclusion that there does seem to be a design floor that manages to show itself just after the guarantee has run out.
I have repeatedly, over the last couple of months, dismantled the rear of the fridge and defrosted the evaporator. On my last defrost I have gone as far as measuring what I believe to be a thermistor located at the top left corner and that seems fine – it has a pair of yellow wires from the bottom red connector.
What I believe to be the heater has a very low resistance and again seems fine – red and black wires from the red connector at the top both going into the bottom right of the heater. The only device that I can’t get a reading from is the pair of wires that appear to enter the top end of the heater, is this where the thermal fuse is located? This device seems to be in parallel with the sensor mounted on the back panel of the fridge itself – which I get a reading from, but the other pair is open circuit.
I have contacted Samsung on more than one occasion, but they are not very forthcoming with information that I can use.
I am also aware that Samsung have updated many of these parts is that
correct and if so, does anyone know why?
Any help would be much appreciated.