I am looking at buying a 2500 Suburban with 160K miles but it has a few issues. One is the service 4wd light comes on and the 4wd switch does not work. It also needs a rear main replacement. But the isssue that concerns me the most is the the AC only blows out the Defrost vent for the most part. A little comes out the face vents, but not much. I researched the topic alot and saw alot of different answers. Just curious what some of you may think or have done as a repair. I saw that it could be anything from a controler issue to a vacum leak in a tube by the battery. I know how to fix the first two issues, but this one seems to be hard to find a true diagnosis.