My 1999 S70T5 AC works great until I get in stop in go traffic when the outside temp is above 90. Then it will not blow cold air. What makes this even stranger is that I can turn off the ignition count to 20 and it will blow freezing cold air. On long highway trips no problem but in rush hour with hot condtions no AC. Anybody got a clue? The dealership cant find the problem.