98 dodge neon defrost and dials?

[diva]

Hi i got a car for 700 and the guy said the dials are in need of being replaced, because they just turn and the only thing that changes is the fan speed and the heat to cool air. but its wintor now and i tried to put the defrost on but nothing happens at all, just the heat is on blowing towards you, but it wont defrost my windows and the window vents dont tur on,and its hard to drive with the windows all foggy in the wintor especially at night with the passing semis -.- So how do i get the defrost working? Is it something under the hood? And my a/c dont work either >.< What do i do, i need defrost to work