GMC Repair: vents, gmc safari, safari van

Question
I have a 1999 gmc safari van with a 4.3 and it is 2 rwd. I have recently replaced the radio in it and about a week after that, when you would turn the knob for the a/c on the a/c would come on but the vents do not change. So it will not blow out the vents facing you. It only blows defrost and at your feet.I hope this kinda makes sense.  I have taken the dash back apart to see if i might have knock something loose but I don't anything in that area of the radio where I was. Might I ask, that switch that controls the vents is vacuum operated right? I do appreciate if you could point me in the right direction. Thank you for your time.

Answer
Hi
It sounds like you have a vacuum leak.
The vacuum line runs from the hvac controller across the passanger side and out into the engine compartment.
As you did dash work, I would REALLY inspect the inside line. I did one once and I hit the vacuum line with my foot and knocked it loose, so you may check in the passenger side foot area, around the glove box.
I really hope this helps.
Good luck
Pawl