It is my brothers soon to be his 93 150. What happens is if we turn the switch to max a/c it will stay on defroust for about 2 seconds then kick on the a/c. Now if I get on it somewhat (2500 to 3000 rpm before it shifts) or if it downshifts going uphill the air will switch to defroust and stay on that till it decides to go back. All this happens so long as we don't turn the dial, if we do it goes to what we turn it to. It has a 302 with the E4OD tranny and 4x4. We are assuming it is the switch itself. Has anyone had this problem and any suggestions will help.