Hi
I have a GE side by side refridgerator model GSS20DBMBWW, and it keeps icing up on the back base of the freezer. When this happens, the fridge side gets warm, and it keeps running all the time. In addition, the fan in the back makes an odd noise. I cleaned the coils which did have some dust, but it still happened. The only thing that temporarily fixes the problem is when I unplug the unit, and leave the freezer door open overnight. This, as you can imagine is a real inconvenience. The problem comes back in a few days.
Could it be a heater problem, and if so, exactly where on the unit do I have to look to see? I am fairly handy, but have never done repairs on a fridge before.
Thanks for your time. 
The problem is a faulty defrost system or a bad main control board. You can find the complete troubleshooting instructions in one of our previous posts: http://forum.appliancepartspros.com/refrigerator-freezer-repair/4221-freezer-fine-refrigerator-too-warm-3.html in the reply addressed to Bohemian.
Here are the break down diagrams for the GE refrigerator http://www.appliancepartspros.com/partsearch/model.aspx?diagram_id=569009&&model_id=210309
Gene.