My '99 is the same way - the two right-most positions (feet + windshield and all-windshield, IIRC) automatically turn the A/C compressor on, and you cannot shut it off by pressing A/C button.

Many cars do this for the all-windshield setting so that drivers who don't understand the complexities of their HVAC systems and controls can still defrost their windshields effectively just by moving the selector to that position.

kpaske - If you have it set on defrost and the A/C light is lit and you still have moisture, then set the temp control to the hot position. If you still have moisture, then maybe your A/C needs recharging or (and this became a family joke after I said it once to my sister in reference to her Cherokee) maybe your flap-valves are not actuating. That is, maybe the flaps in the ventilation ducts are not switching to direct air to the windshield. You should be able to figure out which it is by checking if you're getting airflow and by the temp of the air.