Here's a pic of the blend door which is in the pic on the heater box in the center. The silver tubing is for the A/C evaporator and is just to the left of the blend door. The door is hinged on the right side of the square hole in middle of the heater box. In the pic in this post you can see the square with the one rounded side where the shaft of the electric actuator fits into. This rounded square is one of the two points that makes up the hinge. The rounded square is on the side of the heater box facing the radio, the side of the hinge on the blend door that faces the firewall is just a point. Both pieces of the hinge protrude each through their own holes in the heaterbox to allow the blend door to go up or down. When the blend door is air is forced through the heater core, the velocity of air will hold it up until the van is turned off and the airflow stops, then no heat again. The default position if the actuator fails or if the blend door hinge breaks is to go down thus preventing any air through the heater core and thus cold air though the vents.
The pic below is of the door but its upside down from the way its installed in the view of the heater box.
This pic below and the two above are from 12ounce. The one below shows the reinforced section on a repaired '99 Windstar blend door, aka the "12ounce" method.
