2003 Chevy S-10 6 cyl Four Wheel Drive Automatic 62500 miles
In the past 6 months I have replaced the heater control unit, because it had a vacumn leak, 3 times (at $129 per each unit!). When the audible leak occurs the unit would be locked in the vent only position no matter what I selected with the dial. I tore this last one apart and behind the selector switch where the vacumn lines hook up there is a channeled rubber disk that directs the vacumn to whatever is requested. This disk was covered with a moisture/liquid, thus losing it's seal and creating a leak. A garage thought it was because I had transmission fluid in my transfer case and was sucking some moisture up thru the vaccumn line because of a bad seal. They checked the transfer case and it is in perfect condition. Now they think maybe the intake manifold is seaping coolant somehow and that is getting into the vaccumn line. The problem is that this is a $550 experiment for something that they are not sure off. I have a very little bit of moisture around the gasket now and I haven't added a drop of DexCool to my system ever. So I am hesitant to believe that is the problem. Has anyone ever run into this situation before and maybe steer me in the right direction about where this moisture is coming from and how to fix it?