Need help with a vacuum problem

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Jan 2, 2011 | 04:41 PM

Crawler374

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Need help with a vacuum problem

No not an intake vacuum, the dash air control vacuum. I have traced back my vacuum lines from inside the cab to the firewall, and traced them to the vacuum canister under the hood. There are no cracks, no dry rotted lines. The only one that was dry rotted i replaced, so now i have an extra line and i can't figure out where it goes. My problem is no matter what heater/AC controls i use, air always and only blows through the defrost vents. I can push in the vacuum cylinder under the dash and it blows air through all vents. So here is a pic of the extra line i'm talking about.

The blue line is this pic is the one i replaced.

any help here?

I have a 1992 f350 with a 5.8 351 windsor. I can get more pics if anyone needs any. Thanks for any help!

Jan 3, 2011 | 12:49 AM

mmhoward

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From: Memphis, TN

I'm no pro on this, but I followed Steve83's info and it fixed my problem.

1983 Ford Bronco General Purpose Pics picture | SuperMotors.net

You have to go up in the area where it bundles and cut out some more to make sure you get it back far enough to make sure the weather has not deteriorated the hose.

Jan 3, 2011 | 12:58 AM

LCAM-01XA

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I think you got them lines switched around - the white one should be going to the vacuum servo for the recirculating (fresh-air) door, and the black one is the vacuum supply for the entire HVAC system. So pull the blue line off the black like and connect it to the white line instead, then connect the now-loose black line to any available intake manifold vacuum source (this could be a metal vacuum tree on the intake, or a plastic vacuum manifold on the firewall somewhere).

Jan 4, 2011 | 04:06 PM

Crawler374

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Quote:

Originally Posted by LCAM-01XA

you are exactly right. got that straightened out and i finally found the other end to the black line. got them connected and.........nothing. still the same

Jan 5, 2011 | 01:14 AM

LCAM-01XA

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Did you follow the other piece of the black line all the way to a vacuum tree or a vacuum manifold? It could be that at its very end (actually that would be its start) the black line fell off whatever its vacuum source was...

Jan 5, 2011 | 04:41 AM

Crawler374

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Quote:

Originally Posted by LCAM-01XA

i took it all off to inspect. i also blew through the hoses and sucked in the T connector. all was good. I was able to follow the vacuum from the black line through the firewall and its headed towards the defrost vents in the middle of the dash. It was getting late and i was out of time. I cant just take my dash apart when i want to....

Jan 10, 2011 | 03:09 PM

LCAM-01XA

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Quote:

Originally Posted by Crawler374

Sorry for the late reply, got connection problems for a few days. What I meant was to follow not the part of the black line that goes through the firewall, but the other loose end, the one that goes towards the engine - this is your vacuum source, if there is a problem somewhere there then nothing under the dash will work right.

Also, the line you followed may look like it' heading towards the defrost vents, but before it reaches them it will turn towards the face of the dash and go into the HVAC control assembly (with the ***** you operate) - try pulling that out and see how the connection of the line looks at the back of it, your truck is two years newer than mine and my vacuum lines are like new under the dash so yours should be good too, but one never knows. (You may have to pull the radio out too, to get some more work space for messing with the HVAC stuff.) I would suggest that you unplug the vacuum lines connector from the back of the control assembly and stick a vacuum gauge in its port with the black line in it - if you have vacuum at the connector with the engine running, I'd venture to say the problem is withing your HVAC control assembly.