I used a side-by-side when I first got into kegging. With two temperature controllers I controlled the freezer side and the fridge side. The freezer controller turned the refrigerator on and off. The fridge-side controller controlled a computer fan mounted in the duct between the sides, pulling colder air from the freezer to the fridge. This worked well for lagers at 36F and ales at 46F. The lager side also doubled as a conventional fridge for hops, bottles, etc.