The A/C on my 97 Windstar only blows out the defrost vents, no matter where I set the "output" control. I can't feel any vacuum on any of the tubes of the output control's vacuum harness--nor do I know which one is SUPPOSED to have the vacuum. What should I do? A/C coming out of the defrost vents is better than nothing, in this heat, but it does fog up the windshield in short order. Help!

Check for vacuum leaks. Common problem is the line that comes from the engine into the cabin of the car. It gets hard and brittle and cracks, then no vacuum to power the vent actuator pods.

blower door assembly under dash is broke or resistor burnt out that controls it

The first thing I would do is have the computer checked for trouble codes. The codes will point you in the right direction to look for the problem. The codes may be for something other than the vent problem.
The air is directed thru the heater core and evaporator core and also to the correct vents by blend doors in the ductwork under the dash. They are usually controlled by small electric motors.

The ball is a vacuum tank. It would take the active vacuum line on one side and the other would go to the vacuum line that leads to your ventilation controls. Connect a length of vacuum hose to either side and BLOW through it. If you can't blow through it, that's the side that goes to the engine since it would have a check valve to prevent the vacuum from escaping when the engine is off. If you can blow through both sides, then it doesn't matter which hose goes to which side.

thers a vacuum line under the hood on the drivers side fender its real small and theres vacuum on the back of the climate control its just a matter of chasing it down

If the mode door is vacuum operated, you have a vacuum leak. If it's an electric motor, you have an issue with the motor or controller circuit - or the switch. To properly diagnose you'd need a Tech2 or multiple diagnostic interface and GDS software.

defrost is fail safe mode. cehck for a broken vacuum line from the engine to the heater control head. check vacuum reservoir under hood for leaks.

You have a vacuum leak in the system that controls the vent doors. First check for cracks at the vacuum reservoir, then check the various vacuum hoses and vacuum motors for a leak.
Charlie

Does it still blow out the floor and defrost when you set the switch to those positions or does it alway blow out the defrost no matter what? If you can get air to blow out to the floor, then it sounds like you lost the switch that controls the airflow to the vents. If it only blows out the defrost, then you probably lost the vacuum to all of the switches. When the vacuum is lost, it will only blow out the defrost. Check the smallest line on the vacuum distribution block located in the corner near the brake master cyclinder. That line provides the vacuum to control the direction of airflow within the cabin.

You have a vacuum leak.Defrost is the default postion(no vacuum).
See if you can locate the small black vacuum line that goes inside the vehicle on the passenger side near the heater core. The trace it back,should see it going to a canister then to the intake manifold.Make sure it is not disconnected or broken somewhere.