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I own a 1996 Ford Mustang and when I turn on the Air Conditioner on the upper part of the car, or on cycle it doesn't work through the vents that hit you in the face/chest area. However the vents do work on the windshield and the side windows. Sometimes at random they will kick in and I can get some cold air onto my face and chest area. What is the problem and how do I fix it?
 

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Hi......there are flappers in the system that direct where the air flow goes. Most of these are controlled by either a cable or a vacuum line. The cable stretches or breaks, the vacuum line dry rots and cracks and loses vacuum. The parts are cheap enough, but the labor to replace them might cost a bit. Basically, you have to pull part of or the whole dashboard out, replace the bad part or the switch, and then put it back together again..........that takes at least 3-4 hours usually. Good Luck!!!
 

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the doors that control which ducts the air flows through, are controlled by vacuum motors, which are in turn controlled by the switch on the dash. most likely the motors have gone bad and are not holding vacuum. you can test them easily by taking a length of vacuum lineof the right size, attach it to the vacum motor, and suck on the open end. you should see the motor move. if you seal the vacuum in with your tongue, the motor should remain in place. if it passes these tests, then either the lines to the motors, or the switch is bad. if not then the motor is bad. there is also the possibility that both are bad, so keep that in mind.
 

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Your Vacuum one way valve has failed or vacuum hose has cracked at the motor a Ford mechanic can fix it easily. Default to defrost and when vacuum builds up it changes over. Accelerate and back to defrost seem like what it does?
 

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It is a vacuum related problem...open the hood and look carefully for a loose or broken vacuum line. Look for a 1/4" or smaller plastic line. You may have to take it to a shop for repair as it could also be the control head.
 
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