A/C vacuum problem need advice

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Turbo Zach

Comic Book Super Hero
Sep 8, 2015
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I have developed a vacuum problem. I have a 3.8 turbo engine. I have had some issues with my vents changing from floor to dash vents. Last winter I changed my rearend gear ratio to 3:42. The vents change ok at idle or low rpm. When I am going above 60 mph I am not running very much vacuum, under 10 psi. Do to the higher rpm and turbo. My vents switch back to the floor. Do I need a check valve on my round ball or is this the nature of the beast? The car does not get drivin in cold. Is there a good way to lock it in dash vent position? What are your thoughts on this problem?
 

Texas82GP

Just-a-worm
Apr 3, 2015
7,981
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Spring, Texas
Maybe start with making sure the system holds vacuum with a Mighty-Vac. I'm surprised that 10 in. hg. is insufficient to operate the dash vents. I guess you could take the dash vents and cruise off of manifold vacuum and run them of an electric or belt driven pump. Those are the only ideas that come to my mind.
 

BOXCARS

Master Mechanic
Apr 29, 2017
337
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Yeah, you need a check valve. My car was doing the same thing and I changed a check valve close to the firewall where the vacuum lines go into behind the dash.
 

foxtrot

Royal Smart Person
Dec 19, 2008
1,489
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I believe that I have a Dorman 47149 Vacuum Check Valve installed for my HVAC vacuum. It's installed right before the HVAC hard line under the hood.. Good luck.
 

foxtrot

Royal Smart Person
Dec 19, 2008
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I was mistaken with regards to the install location, it's installed on top of the intake in the vacuum line that feeds the HVAC vacuum ball.
 
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airboatgreg

Comic Book Super Hero
Oct 2, 2016
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Start with check valve. You may think about a larger vacuum reservoir. Find a central vacuum source on engine. Ford actually make a decent check valve
 
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