Forest, there is a vacuum generator in or near the location you describe. It is used to switch the heater/AC from blowing through the dash vents to blowing through the windshield defroster vents. If that is the problem, they are no longer available and you will need to install an electric vacuum pump. Tom had to do that recently and has the part numbers and installation information in this post:
http://www.newellclassic.com/forum/showthread.php?t=997