DESCRIPTION Cherokee and Wrangler use a blend-air heater system. Temperature of air entering passenger compartment is controlled by regulating amount of airflow through heater core and then blending it with a controlled amount of cool air that by-passes the heater core. OPERATION CHEROKEE Mode Control Lever The upper control lever on the control panel operates a vacuum switch on back of control panel. Vacuum switch controls vacuum to defroster, floor and panel vacuum motors, as well as a vacuum- actuated heater coolant control valve. See Figs. 1 and 4. The heater coolant control valve closes when vacuum is applied to it. Temperature Control Lever The lower control lever on the control panel moves a cable that controls the position of the blend-air door in the heater case.