Is there a vacuum that controls which vent the air comes out of defroster only 96 Sebring convertible?

No, a 1996 Chrysler Sebring convertible does not use a vacuum system to control which vents the defroster air comes out of. The airflow direction for the defroster is controlled by flapper doors within the dashboard's ventilation system. These doors are typically operated by electric motors or cables connected to the climate control system's switches, not vacuum.