Side by Side Refrigerator, cools and freezes for several hours, and then stops for several hours, everything melts in freezer before it starts back to cooling. But works great when it is working. It has been checked. Compressor is working, freeon OK, new thermastat and new defrost timer. Still not fixed . What could be the problem?

If all those thing have been checked or are new then your cold control is one of the last things.