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Old 01-17-2008, 08:37 AM   #1
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Join Date: Jan 2008
Location: Nashville
Posts: 243
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Thanks JeepCrawler98 :)

I just wanted to give a thanks to JeepCrawler for posting a response in a vacuum leak thread. My jeep would only blow in defrost. I replaced the AC/Heater control switch and it didn't make a difference. So I figured I had an exhaust leak. But for the life of me, after reading the online service manual (my chrysler one hasn't gotten here yet) I could not find the damn vacuum hose. After searching and reading many threads in the TJ forum, I came across this post.

Most of the time when the TJ HVAC plenum box stops routing air it's because of a vacuum leak. Open the hood and look on the intake manifold - you will see a small hose coming off of it that goes across the firewall to the passenger side. There it Tees into two routes - one going to a vacuum reservoir located below the battery, and one going through the firewall and to the selector knob you see. Inspect the hose - and experiment with blocking off the vacuum reservoir to see if the problem is before the knob, or the knob itself. You may also want to stick a vacuum gauge on there and see where it's registering. It should be around -15psi or so (normal engine vacuum), and when you rev or stop the engine (eliminating vacuum) it should stay there as there is a check valve that should keep the vacuum in (or the pressure out depending on how you look at it) and the vacuum reservoir should last a good while unless there is a leak.
I finally found the vacuum and it was just hanging on the body stablizer bar. Apparently, when I changed my exhaust header, I stuck a random wire that's not doing anything into the vacuum socket on my intake, pull it, stuck in the correct vacuum and now everything is working great. Plus it saved me from tearing my dash apart to trace a leak. Thanks JeepCrawler98

98 Sahara

Peace and be kind - Jerry Garcia
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Old 06-22-2012, 11:53 AM   #2
Join Date: Jun 2012
Posts: 2
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I second that Greg!
Fixed for a 1 foot, 52 cent piece of vacuum hose.
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