Vent control not working in cold weather

I have a 2001 Grand Prix GT and when the weather is cold, my vent control does not work properly. When you switch the vent say from the front window defroster to the vent at your feet, it does not work. The air flow seems to be coming out on all vents. After awhile, as the car warms up, the vent control works properly. My last car was a 94 Grand AM and it had the same problem. It seems the tubing for the vent was not holding the pressure to allow the vents to be changed. I removed some of the plastic tubing and installed a rubber tubing in its place - it worked. My question here is I cannot find the tubing on my 2001 Grand Prix that controls the air vent. Please advise.

Thx

Hmmm! I'm the new one on the block... but if I am not mistaken this post dosen't really belong in this forum... (Introductions)???