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Vents do not switch (not a vacuum leak)

A

Arkansas91XJ

NAXJA Forum User
Location
Arkansas
91 4.0 AW4 4x4

Whenever I switch between the modes (A/C, Vent, Heat, Defrost), the air only blows from the top of the dash. I thought that it was probably a vacuum leak so I was poking around triyng to find it and I couldn't hear it hissing anywhere. I took it down the road, got it to speed, and engaged the cruise and it cruised just fine. If I have a vacuum leak, the cruise doesn't work, right? And if it's definately not a vacuum leak, what's next? I know there is a door shoved up in the dash to control all that, can it seize or something?
 
It CAN be a blend door problem the method of vac leak testing may be a little incomplete.

The cruise side of the vac reservoir and lines to it may be fine.
The HVAC side of the reservoir may have a tink leak (or the hoses to it)

The lack of hissing does not necessarily mean you don't have a leak. I have mentioned this before and there is some disagreement in my method. But it's worked everytime for me.

Get a cigar, cigarette, etc. and fire it up (you don't have to inhale). Take a big toke on it and blow the smoke into one end of any/all your hoses. Look for smoke escaping, if so, there's your leak.

I chased a vac leak in mine for weeks until a mechanic showed me this, saw the smoke, found and fixed the leak. Problem solved. Give it a shot first, easiest way to go. Other wise I don't know squat about blend doors.

Disclaimer: The Surgeon General of the United States would probably not agree with this method, but he don't drive no XJ.
 
The small hard vacuum hose that goes through the firewall and to the heater control has a habit of hardening and breaking. The vacuum leak is not of the magnitude to effect the overall vacuum.

Pull the gauge fascia, then the heater control. Disco the vacuum connector and plug the line at the control. Then go under the hood and use a hand vacuum pump with a gauge and pull a vacuum on the line and make sure there are no leaks. I have seen the silicone gasket on the back of the heater control be defective or the plug not seated all the way.

You will not be able to hear a vacuum leak with the engine running.
 
ParadiseXJ said:
It CAN be a blend door problem the method of vac leak testing may be a little incomplete.

The cruise side of the vac reservoir and lines to it may be fine.
The HVAC side of the reservoir may have a tink leak (or the hoses to it)

The lack of hissing does not necessarily mean you don't have a leak. I have mentioned this before and there is some disagreement in my method. But it's worked everytime for me.

Get a cigar, cigarette, etc. and fire it up (you don't have to inhale). Take a big toke on it and blow the smoke into one end of any/all your hoses. Look for smoke escaping, if so, there's your leak.

I chased a vac leak in mine for weeks until a mechanic showed me this, saw the smoke, found and fixed the leak. Problem solved. Give it a shot first, easiest way to go. Other wise I don't know squat about blend doors.

Disclaimer: The Surgeon General of the United States would probably not agree with this method, but he don't drive no XJ.
Click to expand...

I guess I'll try this way first. I forgot to mention that I had just replaced the NSS and maybe I smashed something pulling the plug back into the bay?
 
danw77 said:
????????????

:doh:
Click to expand...

i had posted it and then realized it wasnt gonna fix his problem, then I was gonna delete it but figured it might be useful to someone who comes across this on searching
 
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