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Answered 2005-07-28 21:00:48

On my 1998 Ford aerostar the direction of air flow is controled by a vacuum motor, the other fords maybe the same. If vacuum is lost to the control switch the vacuum motor will not work. non activated position of motor is defrost position. On my 1998 ford aerostar I found that a vacuum line (note this vacuum line came off of a 3 connection vacuum splitter connection)that ran from engine compartment into firewall was connected inside of ac eveporator plastic cover inside passanger compartment. then the vacuum from there was routed from a plastic outlet and vacuum line, to the ac control switch. Sence I could not get to the inside of evaporator cover without much must work!! I ran a new line around the problem. to determine if this is your problem check for vacuum at little vacuum outlet at bottem of plastic evaporator cover inside passenger compartment maybe your line is just off there. Note, in surching for this problem I also found that a vacuum line that controled rear air flow was folded in half under dash preventing back ac from working properly. Blew heat all the time in back.

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