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.
Do you mean the defroster fan? If so yes if it blows the main engine circuit breaker in the fuse block.
The AC is probably coming through the defroster because the air door is stuck. The door is behind the dash and is vacuum controlled. A vacuum leak or bad door will cause this problem.
A bad heater core / it needs to be replaced
This may be a cause... My wife's 95 contour had to have the vacuum temp settings control unit replace 2 times. If you are constantly changing settings it really blows the valves in the climate control center... Just a thought.
The motor which blows air through the vents.
One reasons a Dodge W 250 defroster may not work is the blower motor relay. This can be replaced easily. If it isn't the relay, there may be a problem in defroster door binding. A mechanic will be able to determine the cause.
the radiotor or the cams
The Bands in the transmission are slipping/ the tranny is bad.
what would cause all power windows to only work once in awhile and defroster to go out on a 1997 dodge intrepid
The most likely is the vacuum line used to operate the swinging doors to redirect airflow is broken or not in place.
could be a vacuum line off
The most likely cause of a 1992 Ford Aerostar stalling while idling is bad spark plugs. The plugs should be changed and the timing checked to resolve the problem.