HVAC Not working correctly???
#1
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Year: 2000
Model: Cherokee
Engine: 4.0
Have noticed in my new to me XJ that when I am cruising at 50+ my air system will act weird. Say I am going down a hill it will stay in the vents into the cabin but when I give it gas to go up a hill or the transmission shifts from 4th to 3rd it will blow air through the defrost vents and then if I let off the gas it will go back to the vents where I have it set. It does this in AC mode and heat mode. If it's in defrost mode it will stay on defrost no matter the speed or gas. 1998 Sport 4.0 with AC
#2
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Location: Los Angeles Ca.
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Model: Cherokee
I think I'm having A similar problem I can hear the vent doors in the –dash opening and closing sometimes. Hope somebody chimes in with a solution without having to rip open the dash or tear out the dash? 90 xj i6 aw4 242 Tc. Does your heat blow hot .?and AC cold?
#4
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Year: 1998 Sport
Model: Cherokee
Engine: 4.0
Sounds like you have a vacuum leak. Start by checking the vacuum ball behind the front bumper on the passenger side. Check it for any cracks or loose hoses. If none fallow the hoses all the way to the firewall. The vacuum is what controls the blend door which controls where the air comes out of. Hope this helps.
#5
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Location: District of Columbia
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Year: 1998
Model: Cherokee (XJ)
Engine: 4.0
^^^ Agreed on the vacuum leak. FYI to the OP, with no vacuum in the system, the HVAC will default to blowing out the defroster. That's why you lose your vacuum when you're going up hill. Since the throttle is open, there's no vacuum in the intake manifold.
#7
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Year: 1999
Model: Cherokee
Engine: 4.0
Here's some photos of the HVAC/Cruise vacuum system in the engine bay - mixed years.
Click the image to make it larger and click it again to make it larger yet.
https://www.cherokeeforum.com/g/album/3212409
Click the image to make it larger and click it again to make it larger yet.
https://www.cherokeeforum.com/g/album/3212409
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#12
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Year: 2000
Model: Cherokee
Engine: 4.0
This? Could that cracked hose be the problem? That's between the body and battery.
Last edited by jpmarine6786; 05-26-2015 at 05:11 PM.