Need Help With Defrost System

I Have A 3.5 Year Old Samsung Fridge/freezer That Has Constant Problems With Ice Building On The Coils. I Am Thinking It Has Something To Do With The Defrost System. The Unit Has Twin Cooling. I Am Not Finding Anything On The Breakdown Diagrams. I Know That The Fan In The Fridge Compartment Is Not Working. Any Help Here Would Be Greatly Appreciated