I think the vacuum line to the heater controls is clogged. The reason I think this is I can draw vacuum at the vacuum line and it will pull vacuum but none of the controls at the heater control will open any of the vacuum motors.

My question is this: How involved is it to replace the vacuum line?
Can I just drill a hole in the firewall and put something different? Maybe some nylon tubing and somehow mate that with the pink "Y" connector behind the heater controls?

It looks like I'd have to take apart the dash to get to that tube.

Any help would be appreciated. Thanks.

try running very low presure air in the line from the engine bay and soap everything at the control. i've found 2 controls leaking at the branch connection the dial looking thing works.

Between the engine and the line that goes through the fire wall there is also a vacuum reservoir (I think a little plastic ball on an 89). These things can go screwy after a while- specifically the check valves in them or the in-line check valve near them. Check the stuff under the hood before you dig into the dash. Dash controls sometimes leak vacuum but they rarely "plug up" in my expereince.

The vacuum resevoir doesn't have a check valve in it does it? I know there is a check valve inline with vacuum line off the plenum but it's doing it's job.. I checked. The vacuum ball is located in the fenders, not on the firewall. I think the little plastic ball you're talking about *is* the check valve, not a resevoir.

The vacuum line itself is plugged, there wouldn't be a reason why anything under the hood would cause the line to be plugged or anything under the hood would fix a plugged line.

I agree with you that they'll leak before they plug up but this one is definately plugged or kinked. i'm pulling vacuum directly off the line that runs through the firewall..

No, I didn't say the reservoir was on the firewall, but since you mention it, yes, in some years it was a little "mailbox" shapped thing above the brake booster on the firewall. Yeah, the check valve is a little tiny thing (FYI- make sure it's "checking" in the right direction). The reservoir is a plastic sphere about 4" around, and it wouldn't surprise me it's inside the fender, although I couldn't remember where it was when I originally posted.

I'm assuming you're only getting air coming out the defroster vents? That's the default on 3rd gens if you've got no vacuum going to the HVAC controls. If it's stuck on some other setting then you may very well have a problem with the selector switch or, like you say, a plugged line. Still, an unplugged/cracked/broken line leaking vacuum is more likely, in my opinion.

I know the line is plugged because I can draw vacuum on the line (yes, this is after the check valve and it only fits one way considering it's 5/16ths on the end that connects to the plenum and dual 1/4" on the other end. And besides, the check valve isn't working, it leaks vacuum/pressure.)
and have the controls on the heater controls disconnected and the line still holds vacuum. I'll have to see if I can blow out whatever is plugging the line..

Like I've said, I know that it's a problem with the line, I just needed to figure out if there was an easy way to replace the line if need be. I know the line is good up to the clog because it will hold vacuum.

Any other ideas?

So I borrowed a compressor today and tried to force air through the supply line from the plenum and backwards from the heater control side as well. Nothing.. It holds pressure up to 30 psi... So back to my original question, how hard is it to replace the line? Can I put a nylon line in place of it and how hard would it be to route the line the same way it's run right now?

I'm thinking it'd be easier to run a nylon line through the firewall, not behind the dash, therefore allowing me to bypass having to take the dash apart and then splice it into the heater control tubing.. Is this feasible or is there an easier way?

-Bruce89TA