air blowing out all vents?
 

I have a 2000 monte carlo LS and air is coming from all vents no matter what setting it is on. I realize most older cars vents are vacuum operated, are the 6th gen ones as well? Any help is greatly appreciated!

I think they run on vacuum, I also think some if not all Chevys default to defroster and foot position as a fail safe.

So I'm not losing my mind....my '06 does the same thing. Kinda annoying on my drive to and from work since it's 75 miles each way. Wish I could just have it off.

The only thing vacuum operated is the HVAC controls for where you want to redirect the air. It is that switch which controls the blend door actuators to open and close which is vacuum operated. This switch only works when the engine is running. If air is blowing through your vents when the car is off it is because the blower motor is still running. Can you select the blower speed with the car off? or is it stuck in the 1st speed? Can you please clarify?

Do you mean a little bit of breeze, like your on the interstate and a little comes through the vents, if you do thats normal my car does the same thing. Air from outside blows in to the fresh air intake. If its like the blower motor is on non stop than that is definitely not normal

Mine does the same thing. If I set it for the floor only, it still sends air through the defroster as well.

The car is only blowing air when I turn the air on, and all 5 speed settings are working. I believe it is defaulting out the defroster and foot vents. It won't redirect the air to any of the settings I choose it stays on the defrost and foot vents. I did find a broken vacuum line under my hood, it is routed along the passenger side strut tower and plugs into the passenger side upper intake. the vacuum line is broken by the battery tray and I haven't found where the rest of it is routed to yet.

well then its that broken vacuum line that is causing your issue as to why it will not redirect the air through the other options. Repair that line and you should be good to go..

my apologies.. that vacuum line comes from the firewall. if you inspect the firewall you will notice a rubber grommet that holds that vacuum line.. and yes the vacuum line goes into the rear of the plenuum along with the brake booster hose.

As logitech said sounds like you found your problem.