Ok this system is controlled by vacuum. The most common failure on this model would be the dash mounted mode switch leaking vacuum from the floor setting selection. The first thing we need to do is verify that the mode actuator is not ruptured and that the mode door is working correctly. To access this valve, you will need to remove the trim underneath the steering column. At this point you should be able to see the actuator. What I would recommend is removing the actuator to verify proper movement of the door, and to check to see if there is any visible damage to the actuator. Here is how to access this point. Feel free to contact me with any questions! Good luck!
Ok, I found it. My concern at this point is that we are even on the right actuator. The actuator with the blue and the red vacuum lines is the defroster actuator. The actuator in question should be the one with a yellow and a brown vacuum line. This would be the mode valve.
DEFINITION: This table shows the state of the vacuum supply at the vacuum ports shown in the Vacuum Routing Diagram for each mode switch position. The port numbers are located on the vacuum rotary (mode) switch.
NOTE: No source vacuum, insufficient source vacuum, or an improperly routed vacuum supply will cause air delivery to be improper.