A/C problem, and Idle problem??? on 2000 Ford Contour

Okay, I'm going to ask both of my questions at one time: First question is, why does my car's a/c only work when it's on "hi"? Doesn't matter if it's heat or a/c actually, it's only blows out air on "hi", the reason I said a/c is because it's summer now. Next question is, when I'm driving, sometimes my car RPM will just "race" like it has a boost or something, it's not a bad thing, I think, I just want to make sure it isn't. Thanks!

Asked by for the 2000 Ford Contour
For the air question is might be the blower motor resistor, its usually behind the glovebox near the blower motor. As far as the engine racing I really don't know.