Air vent control not working

[mlipmd]

I got my AC working, blowing cold air now that I managed to recharge the system, but my problem still remains that my control buttons on the panel won't change the airflow out of the various vents. The fan works well, can change the speed, but it sounds like it's blowing but only a little air comes out of the vents on the dash or down below. This is probably due to a vacuum leak rather than a problem with the electrically operated manifold tucked up underneath the driver's dash, so I want to investigate the vacuum leak first. Can anyone tell me where should be the starting place to look for this leak? All the lines I see look nice and shiny with no holes or cracks in them but obviously I can't see them all. The vacuum pump on the passenger side below the headlight goes on for a few seconds if I turn the key on, then shuts off and does not keep recylcing. At one time it seemed to keep running on and off, sounding like a failing headlight motor but it doesn't do that anymore. I haven't checked the cruise control to see if that works, if not, that could indicate a vacuum leak too.
Thanks.