I have an '87 Chevy 1/2 ton 4x4. I can't get it to switch from heater, to defroster, to vent, etc. The temperature control works fine. I took it apart and found the door which directs the airflow, but i am not sure what actuates it. There is a vacuum line that goes to the right kick panel. The line has a tee, and this line is not attached to anything. It is obviously broken, but I am not sure from where. It appeared to go up toward the passenger speaker in the dash. Is this vacuum line my problem, and if so where does it attach?