I have a 1990 Chevy Lumina-the air conditioning only comes out on the floor and defrost vacuum does not change the servos what is the fix?

its vacuum controled , check vacuum hoses under hood to resivoir then into dash switch if ok dash switch is problem

I have a 1990 Lumina... as per the response of "455" above... I recently had the same problem and eventually found a vacuum leak under the hood near the cruise control solenoid where there is a junction "T" fitting. Repairing that connection, other ones popped up over the next week or two. The car is over 22 years old... things are getting rotten... there may be some more hoses that need to be carefully inspected and replaced. There are some hard plastic hoses as well that get brittle and crack. Some are covered with a black flexible plastic covering... and may hide the cracked plastic hose within. Listen carefully for "HIssssses"... squeeze rubber hoses good and listen for any changes or Hissessss... check the hose and fitting that goes behind the MAP sensor... sometimes the hose is cracked at the fitting itself... you may want to pull the hoses off their fittings to see if they fall apart in your fingers. There is a Big Ball under the left fender... it's a vacuum reservoir... there is a long vacuum hose/tube going to it from the connection "T" near the cruise solenoid... make sure you check it from end to end as well and make sure it's connected up snugly. i hope this helps... good luck... john b.