Dual Evaporator Refrigerator -- Evaporator Coil and drain Freeze up... Internal Fan Operational?
I've got pretty much the same fridge. 



GE Profile. I can tell you that the outlet is at the top and without the ciculator running it will freeze. The circulation fan runs even with the door switch open. Also I think the defrost timer on these are solid state, not the mechanical ones that often fail. There could be a sensor somewhere cousing problems with the defrost cycle but you best course of action, based on the information provided, is to test the fan. If it's DC you can test it with batteries. A 12v DC motor will run on a 9v for testing purposes. It's voltage rating should be written on it. I'm an HVAC tech primarily but also do appliance repair, refrigeration and I'm a licensed electrician though I would never claim to be an electrician.

Unfortunately I have never had any problems with my fridge like you are having so I can't help in more detail.