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just bought 94 ford conversion van. 24,000 miles garage kept etc,etc. just drove it for 1st time. seems when under any type pull the a/c drops from in dash vents to under dash as near as i can tell. it doesnt seem to cut off. just seems to start blowing under dash im pretty certain. called p.o. who told me ford said that was they way they work.has done this since new and he did have it checked. im not sure thats correct though. are you? im thinking vacumn problem possibly. any help? thanks so much.
 

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I used to have an 87 Ford van that did the same thing, I suspected engine vacuum, but it never really concerned me enough to spend alot of time figuring it out.
 

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Let me clarify what mine was doing, when driving along a flat section everything worked fine, but when climbing a hill, the trans would downshift into 2nd and the air would switch to floor vents, at the top of the hill when it shifted back to 3rd ,the air would switch back to the dash vents.... I never heard (nor believe) that this was "normal"
 

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I'm having the same issue with my '94 Plymouth Grand Voyager.

So, thinking on the same lines as you, I changed the vacuum tank & dash control and neither stopped it, however it does not do it as often as before. Also added a fresh charge of R134 (after finding & fixing a leak at the rear line) which seemed to help, too.

But, bottom line - it still cuts out at the dash and blows at the floor & W/S when the trans drops out of overdrive and into low gear, like when going up a long hill on the interstate while using the cruise control.

Seems odd - but maybe this is "normal" ??

I'm posting to simply put my name out there in case anyone has any ideas.

~jeff
 

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Discussion Starter #5
seems we all have the same problem. if it is a problem! just doesnt seem right. seems to be fine when in high gear and drops when trans.drops. hopefully someone will provide us with more. ive never had 1 do this and have had many vans.talked to guy today who said his crown victoria does same thing. maybe its ok. thanks.
 

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there is a one way valve in the vacuam system that keeps the vacuam from going down under accelaration.when u accalerate u lose vacuam and the one way valve and vacuam resivor help to mantain a constant flow of vacuam to keep the ac doors from changeing positions.under total lose of vacuam all air will flow out the defrosters
 

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67 coupe, 69 Sportsroof, 86 hatchback
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I second Mike. Suspect a vacuum leak that's not bad enough to affect normal operation until the engine experiences a low vacuum situation, such as a steep hill. Second suspect is a faulty vaccum check valve in the hose to the vacuum resevoir. Third is the vacuum resevoir itself leaking.
And no they are not "designed" to do that. The vacuum resevoir system was designed to overcome the exact problems you mention. Though the resevoir does have a limited capacity and on VERY long hillclimbs you may experience the same thing. You can duplicate the symptoms with the vehicle idling in the driveway. Just unplug the vacuum line that comes from the resevoir and leads to the heater/AC controls.
 
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