What does it mean when the car overheats only when the AC is on?

 

Sounds like your fans aren't kicking on when you turn on the AC. Pop the hood and sit in the car witht he door open then turn on the AC, should clearly hear the fans kicking in (they are very loud on our cars). You can always look under the hood and visually see if they are kicking in too.

 

OK, I'll check it out. Thanks.