Sounds like you have automate climate control (digital display). In which case, the number one failure is the vacuum manifold that plugs into the a/c controller. It is clear, has a single nut on a stud that holds it to the front of the controller- and the plastic/rubber manifold turns to mush over time and either leaks, or plugs up- the only reasonable fix I know of is to bypass that entire manifold by removing the controller and running vacuum lines inside directly to their sources. I've done a dozen or so this way- I use windshield washer rubber hose to splice or lengthen vacuum lines, they can be slipped right over top of colored lines, and no clamps required since it is vacuum. If you go this route, just be sure to match all color coded vacuum lines- do them one at a time.