I have a 1999 ford expidition the a/c works in the rear but not in the front it blows heat

The blend door actuator is located in the left rear quater panel. It's right there when you remove the trim panel (left side rear) Below is a picture of it when panel is removed along with another picture of the air duct system. I also gave you a picture of the connector at the actuator. Make sure you are geting power and test opening and closing. Worst case you could make the blend door stay to where you are geting heat until you can repair the problem...

This does NOT answer your problem BUT, Ford Windstars have a SAFETY RECALL to repair the rear axle. CHECK WITH FORD TO SEE IF YOUR VEHICLE IS AFFECTED. An individual was killed in MASS when the rear axle failed.
Louie Almond

have the front blend door and actuator inspected to see if operational.

try changing the thermostat if that doesn't help check for air in the cooling system

you may have a broken blend door. the only way this gets repaired is to remove the dash. This is best done by a reputable shop. Very tricky.

there is a white box under dash that controls the hot and cold air. it has wires running to it. this has to be replaced.

somewhere in the cabin there is a panel, behind it there will be a small vacuum valve that opens duct heat/cool for the back. I had it go bad in a windstar and stuck on heat, too lazy to replace so i'd pull panel and manually move it once or twice a year

try this first. The aspirator grille is on the instrument panel and looks like a tiny regidter, maybe 1 1/2 inch by 1 inch.

Check for proper connection of the in-car temperature aspirator tube. Refer to the following Service Procedure for details.
SERVICE PROCEDURE

1. Cut a piece of toilet paper or tissue paper about 3.7x3.7 cm (1.5x1.5") (paper towel will not work).
2. Turn the key on and turn fan speed to HIGH.
3. Select PANEL or VENT mode.
4. Place the piece of tissue paper over the aspirator grille opening in the bezel. If aspiration (suction) is present, the tissue paper should stick to the aspirator grille.
5. Turn the fan OFF. The tissue paper should fall off.
6. If the tissue paper falls off the aspirator grille while the fan is on HIGH, check that the aspirator tube is properly connected at the right bottom corner of the front heater. The black connector on the white flexible tube should be snapped over the black tube connected to the heater plenum. Also, check for kinks and cuts in the aspirator tube.

The hot and cold air in the front is controlled by an actuator in the dash. The temp controller is working as designed because the back is working fine. You need to take to local shop to have the vent actuator or heater control box inside changed out. Then the tempaturer controller has to be reset. Good luck

its a very hard job to explain how to do i highly suggest you take if to your mechanic to fix a very technical complicated job to do your self .