The controls of the heating and ventilation system with air conditioning (A/C) are shown in Fig. 4-23. The heater box contains the heater core and three control doors operated by the control head to regulate air temperature and air flow. The fresh air blower housing contains the air conditioning evaporator and a control door for air recirculation. All control doors except the blending door are activated by vacuum servos controlled by the top lever of the control head. The blending door for the heater core is connected to the bottom lever of the control head by a cable.
Insufficient heater or air conditioner output, or air flow that does not correspond to control lever position may be caused by problems with the vacuum system. Check the vacuum system as described below before assuming that another component is faulty.
