Yesterday I fixed a GE HotPoint side by side refrigerator. It was model number CSX22GR. It was freezing up and building up frost and ice but was not cooling the refrigerator side. Most people don't know it but frost free refrigerators have heaters in them that stop them from icing up. When they ice up they stop the designed transfer balance of cold air between the freezer side and refrigerator side.

Sometimes the thermostat goes out, sometimes the thermostat goes out and they even have a timer that can fail and crate the problem. At either rate, the repair should cost you less than $100 if you do it yourself.