hello all! i have a 1991 chevy burb that runs like a champ but is very moody. the other day the a/c was working fine and blowing as cold as ever. but when i restarted it, the A/C no longer worked. the rear blows just fine, but the front does not blow at all. i checked all of the fuses and they are all fine. any ideas? why would it just quit all of a sudden?