System Description
The heater system provides heating, ventilation, and windshield and front side window defogging. One 4-position switch controls the front blower and another controls the rear blower.
System does not use hot water control valve; coolant circulation keeps heater cores hot at all times. Air is distributed through heater outlets and defroster and vent ducts.
Vacuum-actuated doors control temperature and airflow modes. See Fig 1. A slide potentiometer activates a motor-actuated temperature door, which controls airflow through the heater cores.