Vent airflow changes when accelerating

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Jul 6, 2004 | 11:45 PM

yooh11

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Joined: Nov 2003

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Vent airflow changes when accelerating

I have a 2000 Expedition. When I have the fan or ac on blowing towards the front and then accelerate, the air stops blowing towards the front and blows in the defrost vents. If I let off the gas, it will blow towards the front again. What is this caused from?

Jul 7, 2004 | 10:00 AM

ckrichard

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Joined: Mar 2002

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From: Conroe, TX

My mom's Expedition has the same exact problem. It took me a long time to figgure it out, but what is causing the the door to move is vacuum, or the lack there of. The door that controls where the air goes is controled by vacuum, when you step on the gas the engine vacuum decreases and causes the door to return to the stock location, defrost vents. This is why when you let off the gas and the vacuum returns, the door moves back to the selected position. The sorce of this problem is usualy found in the vacuum resivoir, or a loose vacuum line. The best place to start is under the hood. First, start the truck, turn the the a/c on, and open the hood. Next, while standing at the rear, passenger side of the hood and facing the same way as the truck, look under the battery. You are looking for any loose or damaged vacuum lines. If you have real good hearing you will beable to hear air being sucked in. If one of the lines is lose just reconnect it and see if that fixes the problem. If it doesn't, or just makes it a little better, then the resivoir is cracked.

Chris