cjb7804

Got a stumper that I can't figure out. I will have my climate control on either A/C or vent. (anything to put it out the vent), and it will blow fine, untill I pull a hill and then it will switch to the defrost and floor ducts (I believe it blows out the floor also) and then when I get done pulling the hill, it goes right back to blowing out the vent. I've looked for a vaccuum leak and can't find anyting, and I've also checked the vaccuum reservoir behind the glove box and it seems to hold vaccuum just fine. I'm showing about 14.5 in./hg on my vaccuum guage. Not for sure what else to check. Hoping that you guys might have some other ideas for me. By the way my car is a 2000 GT w/4.6l.