Why does my cars heat/air only blow through the floor vents? I have checked for vacuum leaks from throttle body to firewall, behind the glove box, and behind stereo/heat/air control panel. No vacuum leaks, everything is connected. Still blows hot/cold, as well as hi-lo, but will not move to defrost, or dash vents.
Keywords:mustang
Air distribution within the vehicle is determined by the function selector switch position. Airflow control doors are used to direct airflow within the air plenum chamber. Vacuum control motors (18A318) are used to position these airflow control doors.
So I would think if there are no vacuum leaks in the system that one of these vacuum control motors are bad or the linkage is broken.
If you have recently had some stereo or alarm work done, i would check those areas first. Might be as simple as one of those vacuum lines being knocked off.
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