Mine is a RS21 DCNS, but the chances are the 'EVAP' compartment is frozen up at the rear interior of the Fridge compartment. I called out a Samsung engineer who charged me £135 to fit a new 'modified' unit, but 6 months later it froze up again. You can quite easily fix it yourself. Take out all the fridge shelves, and at the bottom you will see the water tank (winding pipe). Behind it is the unit that is frozen up. Undo the 4 screws that hold it in place, take the central light panel off (one screw at the top, then pull the plastic cover off) then 3 screws behind and the 2 screws that hold on the water tank.. It might take some time to get the units out, as they are probably frozen in. When you do prise them out, I used a hairdryer to defrost and it is all working again after that. Equally, if you do not want dismantle, just do a full defrost over a day or so, but the unit is tightly enclosed and you will need to really leave it a long tinme to defrost properly.
Hope this helps
Bill H, December 2007