If by freezing up you are talking about the fridge section behind the salad drawers then that could be the defrost sensor, evaporator cover, thermal fuse, either the drain heater or evaporator heater at fault. All of which sit behind the bottom 2 drawers in the bttom of the fridge, the evaporator cover is large White vented panel behind the water tank.
Hope this helps
Simon Robinson. Datar18 at aol dot com, February 2010