Is the heater ac vent on my 92 delta 88 ran by a vacuum line my air is coming out the defrost and wont change to vent?

Yes, the heater AC vent system in your 1992 Delta 88 is controlled by vacuum lines. If your air is only coming out of the defrost vents and won't switch to the vent setting, it could indicate a vacuum leak or a faulty actuator that controls the airflow direction. Check for any disconnected or damaged vacuum lines, and inspect the actuator for proper operation. Addressing these issues should help restore proper airflow functionality.