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Smokin
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530 Posts
Discussion Starter #1
My brother has a 02 7.3 and when puts it in 4x4 the air conditioning stops blowing through the dash vents and starts blowing through his defrost. What in the world could be causing this? I have no clue. Has anyone else seen or even heared of this?
 

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OBS
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403 Posts
Actually my truck was doing the same thing only all the time. different prob, but mine was fixed when I put new vaccum pump on. Sorry no help
 

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Registered
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116 Posts
I have the same problem, I just haven't fixed it yet. I saw on another thread that it is a vacuum issue. Have him check the vacuum lines for the autolock hubs. If they are leaking, the a/c will do that. It might be somewhere else in the 4X system but that is the main source that I have heard of.
 

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In the passing lane
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1,453 Posts
Mine does the same thing I changed my hubs over with winch hubs so I wonder if I just disconnet the vacuum lines all together for 4 wheeldrive if that will fix it.

anybody know how to d that?
 

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Registered
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1,585 Posts
the vacume hose going down to the front axle might have come off the vacume module , check to see if it came off
 

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Smokin
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530 Posts
Discussion Starter #6
so it is going to be a vacuum leak all together. I guess I will start at the hubs and work up.
 

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TDG Mafia - Booze Runner
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3,705 Posts
Yep it is a vacuum leak. Most of the time it is the inner hub seal or diaphram that becomes worn and leaks. I had to do mine and know of many others that have had to replace theirs as well...
 

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Registered
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170 Posts
yes. check ur vacuum line on the driver side axle. my buddies just did that the other day.
 

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TDG Mafia Member # 37
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901 Posts
Mine just started doing this also but mine is staying on the defrost all the time. Would mine be the vac lines or the vac pump as stated above? Guess I 'll have to do some investigating. Gene :mafia
 

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Senior Member
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461 Posts
The HVAC system is designed to default to the defrost vents in the case of low or absent vacuum ...i think as a safety measure. The seals inside the vacuum actuated 4x4 hubs go bad, or you may have a torn/split/missing vacuum line all together.

Here's an article from 'that site' that details removal of the hub. This is replace the actual hub, but a seal replacement would involve the same.

http://superdutydiesel.com/wiki2/tiki-read_article.php?articleId=35

I feel like i remember a much better article than that that I read one time, but I can't find it again.

Good luck,
paul
 

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In the passing lane
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1,453 Posts
so where does the vacuum line go from the axle, is it possibble to block it off somewhere?
 
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