I think I have my answer, but I don't know how to fix it or where to look: My front ac blows whatever the outside temp is, the rear is fine. I refilled the system and plugged a leaky schraeder valve with a short bolt and Teflon tape instead of the plastic cap...no mo leak. (it will get fixed right, but it works fine for now!). When I'm driving with the blower off, I can feel the breeze from under the dash. Most noticeable on those really cold mornings ( as cold as so cal gets anyways). In the summer, I just get the outside heat rolling in. Where is the outside vent valve located on a 99 Burban? I've looked and found nothing and my Haynes manual...well, it's a Haynes manual. Thanks!