My vac valve is stuck flowing to defrost vents and wont change. After searching and reading im afraid ive got a vac leak but i hear no hissing from control unit.
My question is can I use a vaccume guage on vac line in engine bay that leads to the vac valve behind control to varify//trouble shoot...??
I dont really understand how the single vac line feeding the valve switches the air flow to the different locations(feet,vents,defrost) by me sliding the leaver. An explaination would really help me...
Also one last thing..if i do have a vac leak on the valve, could that effect engine idle/performance??
These are probably very basic questions but your help would be greatly appreciated!!

 

That line is made of a hard plastic that gets brittle over time. It may be cracked or broken in half. That's why your vents are stuck on defrost; I believe that's the default setting when there is no vacuum in the system, but I could be wrong. Best thing to do is trace it down to where it enters the car, leave a few inches there and remove the rest up to the plenum, and get some new rubber hose that has the same inner diameter as the outer diameter on the remaining plastic, and fix it. There's a little disc on the vent selector in the car and depending where that disc is positioned, depends on where the vacuum flows to the actuators in the dash to open the vents. Also, if it is broke, it's a vacuum leak; a small one, but a leak nonetheless and may be making your engine run a little worse.

 

Typically a vacuum leak will cause the engine to idle higher, as in 1000-2000rpm in park. I think I've seen mine hit 2100 with a vacuum leak. It's very frustrating trying to drive it like that. When not on the throttle, but still moving, it will typically idle right at that point where the exhaust resonates in the cabin. It's also harder to stop the car.

I know the last time my vents didn't work, it was because the plastic line fell on the exhaust manifold and it melted a hole in it.

 

If it's stuck open then it could not be broken, they close with no vacuum. probably a clog or something?

 

Thank you guys for the quick response, sounds like a trip to napa for some new vac hose..

 

Consider the following as well:

https://www.thirdgen.org/forums/inte...ctor-disc.html

JamesC