I played with this a little since I turned my bar fridge into my fermenation chamber. I was hoping to use the freezer section for beer storage. With the fridge being controlled at 62*F, the freezer section now stays between 35-40*F, depending on how often the doors are opened.
Like the others have said, these are not independently controlled, so you basically just have to control the fridge side and see what the freezer side stays at. A lot of refrigerator have manual dampers that control how much of the air flow goes to the fridge, so if yours is this way you can close this damper down to restrict flow to the fridge.