refrigerator freezing food

My Frigidaire is a 2003 model, side by side unit. The food in the refrigerator side is freezing up and the freezer is frozen as usual. Any help as to what my problem could be. The coils and the defrost heater were frozen over the first time I checked the freezer. I unplugged it and let it defrost. I turned down the settings to the warmest possible. No more icing over, but the food in the refrigerator freezes up after a couple of days.