kenmore refrigerator is icing up in evaporator coil area?

hello I have a kenmore refrigerator model 596.5039200. The problem is ice has built up in the evaporator coil and it is not cooling properly. At first I thought it was because the circulating fan was not running and it caused this problem, but I have already bought a new fan and replaced it. When I put this new fan on, the fan still didn't run. I was wondering if the fan goes on and off or does it contiusly runs for it to operate properly. If you have any suggestions on this problem your advice would be great. thanks