Problem with ge profile fridge

Question

This has happened multiple times, the fan between the frezzer and the fridge part freezes up, then the top part of the fridge gets hot. Do you have any idea why the fan freezes up? I have learned to take the bottom out of the fridge part and defrost with a hair dryer, but at times I have had to throw out all the food on the top. I now keep a thermometer in the fridge.