Hi Everyone,

I am trying to track down a vacuum leak, I've been dealing with it for some time now and want to get to the bottom of it. I have searched for hours on this forum and others but haven't made any progress.

The main symptom is that the heat/air is only coming out through the defrost vents. There also doesn't appear to be any significant CCV vacuum.

What I've done:

• Pulled all the lines and checked for holes and cracks. Only found one tiny one and I sealed it.
• Ghetto smoke test, pulled the line at the canister and blew cigar smoke into the system and checked for it leaking anywhere. Smoke only came out into the air box. Normal?
• Pulled the HVAC controls off the dash, the backside looks normal to me.
• Pulled and tested the Check Valve near the brake booster... works as it should.
• Edit: Vacuum ball was checked and seems fine as well.

What are my next steps? Replace everything with the thought that I missed a small hole or crack? Are there vacuum lines in the cabin area/under the dash? I was confident the smoke test would reveal something, but no smoke anywhere in the engine bay or cabin... just came out the air box.

I'm kind of at a loss, it doesn't seem to be that complicated of a system.

Unless I missed it I don't see you saying anything about the vacuum ball behind the bumper. Maybe some of this will help?

https://www.jeepforum.com/forum/f11/...ervoir-838489/

apply a vacuum gauge, and choke off suspect areas

Thanks, the vacuum ball does not show any signs of a leak either

I would be inclined to tee into a known good vacuum line, and connect it up where you want it, see if that makes things work.
Fault could be elswhere, jammed flap, broken plastic. vacuum line fault finding can be confusing
be systematic...write the name on tape of each vacuum line
soapy water, and flex each line individually etc etc

The vacuum ***** can leak internally.

Do this. Buy a cheap vacuum pump kit from the parts store and start testing.

You say your HVAC controls don't work. You could determine the vacuum leak is upstream or downstream of where it tee's off into the firewall by applying ~20 in-Hg to the vacuum line then trying to actuate the vents. If the vents work you know that section of vacuum line is good. Use this logic to eliminate sections of the system to find exactly where its leaking.

Also, don't trust check valves that seem good by blowing through them! I thought mine one of mine was good but when tested with a gauge it would only hold about 5 in-Hg.

Thanks for all the reply's and suggestions. Ill track down a vacuum pump kit/ gauge and start there. Ill report back if I have any luck