’99 expedition A/C

OK, here's the thing. I have a 1999 expedition eddie bauer with digital AC control, and when the a/c is on it blows hot air. I know the actual air conditioning works, the bottom line on the a/c is cold even when there is hot air coming out of the vents. it looks to me as if whatever it is that switches from hot to cold is busted, does anyone know whether it's vacuum or motor controlled? I didn't do it. *nodnod*