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Apr 26, 2012 | 08:04 PM

Big pappa

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Joined: Apr 2012

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Help me please...

I have a 2001 v10 4x4 92000 miles. My air keeps going to defrost unless I turn my 4 wheel drive on then it comes out the vents. Drive down the road back to defrost. Driving me crazy........

Apr 26, 2012 | 09:49 PM

Psyclopse

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Joined: Jan 2012

Posts: 1,176

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From: Indiana

Sounds like you have a vacuum leak somewhere. My bet would be the vacuum lines going to the hubs. They seem to get brittle more than any of the others due to the conditions they see.

Apr 27, 2012 | 12:02 AM

The_Punisher

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x2 on the lines.
I have seen the seal in hubs fail every now and again

Apr 27, 2012 | 08:36 AM

Big pappa

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Thank you, I'm gonna check it out ASAP.... Gets hot down here in ga.....

Apr 27, 2012 | 08:59 AM

redford

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Joined: Sep 2000

Posts: 23,174

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From: Stephensville WI

The HVAC system in these trucks is vacuum operated. If the system detects there is not enough vacuum present to operate the system it goes into a default mode, which (as you have seen) is blow through the defroster vents. It is a safety feature.

The fact that the system returns to normal when your front hubs are locked is potentially a huge clue.