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Unread 07-16-2013, 07:08 AM   #1
Octotat
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1995 ZJ 
 
Join Date: Oct 2012
Location: Chattanooga, TN
Posts: 60
Haunted Vent Control

This may need a priest more than a mechanic, but I think the vent control on my ZJ is haunted. I put it on dash vent and the thing cycles back and forth betweed the dash ventins and defrosting vents. I can hear the vent control flap opening and closing.

Can I just shoot holy water down the vent, or should I wash the whole rig in it?

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Unread 07-16-2013, 07:54 AM   #2
dellis
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1998 ZJ 
 
Join Date: Feb 2013
Location: Vienna, VA
Posts: 313
It is switching to the defrost vents when you are accelerating the car, then switches back to your front vents when you let off the gas, right?

If so, it is caused by a vacuum leak that is most likely on the vacuum line that runs from your intake manifold, along your firewall, and down the left fender toward your battery, terminating in a container below your battery called a vacuum reservoir.

Most of the time, your leak will be because the vacuum line that goes to your HVAC becomes brittle and often cracks (it looks like the image below, although this is from a Cherokee rather than a Grand Cherokee). It is a 1mm ID x 3mm OD hose, if I recall, about the size of a fuel line for garden equipment. If that is your break, you can replace it or (alternatively), put some shrink tube over it and create a new exterior sleeve.



If that's not it, you would need to search for the leak visually, use smoke to find the leak, or use a mityvac to test for the leak.
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Unread 07-16-2013, 09:28 AM   #3
Octotat
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1995 ZJ 
 
Join Date: Oct 2012
Location: Chattanooga, TN
Posts: 60
Thanks! I didn't realize this system was vacuum controlled. I'll inspect and replace the line.

This sure beats doing a Seance!

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Unread 07-16-2013, 04:40 PM   #4
dusterdude
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1996 ZJ 
 
Join Date: Jan 2012
Location: hopewell, va
Posts: 2,044
Hell no,seances are cool
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Unread 07-18-2013, 01:54 PM   #5
capcyclone
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1998 ZJ 
 
Join Date: May 2011
Location: Phoenix, AZ
Posts: 233
Let us know if this fixed your issue Octotat. I have a friend with a ZJ that is having an issue similar to what was described.
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Unread 07-19-2013, 10:14 AM   #6
JeepNicholson
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1996 ZJ 
 
Join Date: Apr 2013
Location: Burbank, OH
Posts: 755
My old Dodge Ram had this problem (as well as a similar vacuum system to my ZJ). Turned out a mouse had chewed through one of the tubes, fixed it easily with some shrink tubing like mentioned above, worked great.
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Unread 07-19-2013, 12:34 PM   #7
Octotat
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1995 ZJ 
 
Join Date: Oct 2012
Location: Chattanooga, TN
Posts: 60
Oddly, it only does it when I'm running just the fan on "vent", but when I ran A/C, it didn't do it

Haven't had a chance to chase it down, but hopefully will this weekend
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Unread 07-19-2013, 04:10 PM   #8
congerz83
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1996 ZJ 
 
Join Date: Jun 2011
Location: Congers, NY
Posts: 348
It's a vacuum leak. Mopar makes a check valve that solves everything. Look at my profile and find the thread that I started about "Heatflow under acceleration".... Works like a charm
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Unread 07-19-2013, 04:12 PM   #9
congerz83
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1996 ZJ 
 
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Location: Congers, NY
Posts: 348
http://www.jeepforum.com/forum/f13/h...ation-1458659/
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