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povchrisw 03-29-2012 08:18 AM

heating issue
just bought a 2005 lj about a month ago, iv search but cant find anyone with the same issue. after about 5 miles of driving i seem to lose about half or more of flow threw my vents. the defrost seems a little air moving threw it and if i turn it to the head vents no air moves threw. iv looked under the hood and seem to have no connection issues or cracks. any thoughts before i tear apart the dash?

Shelby427 03-29-2012 02:11 PM

Start at the other end, the engine. It sounds like you have a vacuum leak.
If it's a 4.0 look at the intake manifold, towards the rear. You'll see a vacuum hose coming off of it to the firewall. Follow it. It splits off about mid cowl. One half goes to run your vacuum controls for the doors in the heater-a/c case. The other half runs over to and underneath the battery tray, to the vacuum reservoir. Common problem.

You start up, lots of vacuum pressure, enough to fill the reservoir and compensate for the leak. Start down the road, vacuum pressure drops. Now it can't cover for the leak. Once the reservoir runs out the leak is more then the engine vacuum can supply, and one or more of the doors in the case close and you get no airflow through the vents.

If you get a bad enough leak, only air flow will come out the defrosters.

povchrisw 03-29-2012 02:29 PM

thanks, ill go at it tomorrow when i have some time.. does the resivor bleed off air after shutting the engine off? if not then im sure thats where the problem is

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