Cruise Control Systems: Operation

The control unit, using a signal from speedometer speed sensor, compares the car's true speed to cruise control speed selected by driver. The control unit then either turns on vacuum pump which causes the vacuum servo to open the throttle, or opens a vent at pump which bleeds air into vacuum lines to release throttle and slow the car. If driver steps on either brake pedal or clutch pedal, a combination vacuum vent valve and electric switch vents the vacuum system and switches off cruise control.