A/C vents don't work

[Red_GTP]

Hi all !! I'm new here and am looking for some guidance.

My air conditioner vent controls suddenly don't work. It appears to be vacuum related, because I can suck on the main (purple) line going to the vent selector switch and all the flappers work correctly as I turn the switch (as long as I continue to apply suction). But if left to function off of engine vacuum, it blows air out of all the vents, all the time. There is just a little bit of vacuum in the line - you can hear it, you can just barely feel it if I "tap" my finger on the line, so it doesn't seem to be entirely disconnected from the vacuum source.

Where does the A/C selector switch get it's vacuum from? I've only traced the line as far as the wiring harness bundle going from the passenger side leg area, and it looks as if it goes down and forward through the firewall. I checked the engine comparment and there are no lines that are obviously disconnected.

Anyone have a clue as to where I should look/what I should do next?

TIA

[drdumais]

My 1999 GTP acts similar to yours. The automatic climate control system doesn't switch between vents (i.e. defrost, feet, vent, or by-level) it's stuck on by-level. I'm looking into it this weekend I'll reply my findings.

[Red_GTP]

Actually, I got mine fixed this past weekend and meant to update this news forum on Monday.

The vacuum line that controls the vents (defrost, feet, bi-level, etc) attaches to the actual control switch via the purple lead. The purple line attaches to a black vacuum line that is wrapped into a large electric wiring harness that goes through the firewall above about where a passenger's left foot would be as they sit in the seat. This wiring harness comes out in the engine compartment and goes into the bottom of the main relay/fuse box on the passenger side of the engine compartment just behind and above the battery.

If you look at this large bundle of wires where it comes "unwrapped" and splits into the many wires going into the relay box, you will see the black vacuum line. It sort of snakes around for a few inches, then goes into a "T" fitting. One side of the "T" fitting goes to a vacuum line that goes up toward the windshield, then across the top of the engine to a device on top of the throttle body(?) where other vacuum sources originate/terminate. The other leg of that "T" fitting disappears forward, behind the battery tray like it is feeding up toward the passenger side headlight assembly. (No idea where it goes, what it does)

It turns out that my problem was that this section of vacuum line got crushed under the battery, or the battery tray. I can only assume it has been this way for a while, but finally cut through a few weekends ago, because the battery hasn't been out of the car in about a year. (Hmmm, ...I did have the alternator replaced [no output] along with the serpentine belts about a month ago....)

With no vacuum to the control switch, the "default" air circulation is to your feet, through the main vents and to the windshield, regardless of switch position. I recommend that you pull the glove box and it's facing (about 6-8 small hex-head screws) and locate the purple vacuum line. Disconnect it from the black line heading through the firewall and suck on it as you change the vent control position. If your problem is being caused by a lack of vacuum, this will tell you. If it's the case, trace the vacuum line as it comes out of the wiring harness and see if it's broken anywhere, and then trace it to the top of the engine. If all is OK here, you may need to pull the W/S washer reservoir, shift the relay box to get the battery out, and the battery tray to inspect/repair the rest of the vacuum line.

If no vacuum leaks, I guess it can only be the switch. To remove the switch, you have to pull the entire dashboard faschia. This was no fun, and in my case a completely un-necessary task, as the switch checked out OK.

Good luck!!