An automatic control system for regulating the temperature of the passenger compartment in an automotive vehicle is simplified and improved by the use of a power servomotor having a vacuum motor, an electrical programmer, and a diverter valve as component parts thereof. The servomotor controls the position of a plenum mounted air blend door regulating the passage of cold, tempered, or heated air into the passenger compartment. The servomotor also controls the position of the electrical programmer which in turn controls desired blower speeds and certain other system functions. The servomotor further controls the position of the linear diverter valve which ports vacuum in accordance with predetermined conditions to other vacuum actuated motors employed in the system.