can't select vents

i can't select between the front/heater/defroster vents. the blower, AC, heater and off all work, i just can't select which vent for air to flow through.

You've got a broken or loose vacuum line somewhere. All the vent movements are controlled by vacuum.

You'll need to run the vacuum lines under the dash.

Check the thin plastic vacuum tubing (about 2 feet long) going from top left side of engine near pcv valve, across top of engine and down towards coolant overflow tank. No need to mess with dash. Remove engine cover to replace. Heat from engine brittles the plastic over time and it breaks.

GM part number: 15967970
Description: 9.281 hose
Cost: $7 at local dealer

Let me know if this works for you....

I have had the same problem repaired twice, both times it was that vacuum hose. My vent control switch sticks on defrost while this hose is broken.

Rather than go back to the shop, I'm trying to fix this myself. I've found the hose, but can't find where it plugs back in again. I notice you mention near the PCV valve and near the coolant overflow tank, but I don't find anywhere for this hose to plug in near either of those. Would it be possible for you to be a little bit more descriptive?

Regards,
Jeff

I am an owner of a 1998 Chevy Astro with rear heat and rear air. My problem was only cold air out of the rear heat and only the front defrost vents worked and the temperture selector not switching for hot to cold. I will try to be as detailed as possible. Lift the hood, and look at the large black box on the top left side of the engine. Just behind the AC reservoir, there is a vacuum line attached to the large black box on top right side, that looks like a Tee fitting with three connections. One went to the float switch on the bottom right of the larger black box near back, the other goes straight down to the vacuum ball located on the frame of the vehicle (underneath). The last is a thin vacuum line that looks like an electrical wire. Pull on all three lines one at a time. If one pulls all the way up to you, that is the broken one. The thin vacuum was broken in half on my Astro. The fix was to remove the air filter tube (the 3" flex tube that goes to the backside of the air filter box). Once removed, look for a flexible black tubing about a 1/2 inch round that should look empty because your line is broken. Pull the tubing to reveal the other half of the hose and reconnect with tubing that will fit over the thin black wire. Not sure what size, but what I did notice is that this was probably the same problem that GM fixed before when the vehicle was under warranty because my line looked repaired but was broken in a different spot. Before I reinstalled the air box tubing, I did wrap the entire flex tubing line with aluminum foil to help block the heat. I am not a professional, but I tried this and it worked for me. Good luck. This. feels like the scene in Independence Day when they figured out how to bring down the spaceships in the sky. Good luck