Lately I've noticed that my refrigerator (Whirlpool side-by-side fridge/freezer, about 5 years old) is freezing vegetables located in the two crisper drawers in the bottom. Liquids, including plain water, located on any of the shelves remains liquid. I've adjusted the temperature control, but it's not clear which setting is colder (it's numbered 1 through 9). I've tried it both ways without any obvious difference. I know colder air settles to the bottom, but this "feels" like a bad temperature sensor or a failed shut-off switch that keeps it running longer than necessary. Any suggestions on what might be wrong?