* Driver Input: You set the desired speed using the cruise control stalk on the steering column. This sends electrical signals to the control unit.
* Control Unit: The cruise control's electronic control unit (ECU) receives these signals and monitors vehicle speed via a sensor (likely a Vehicle Speed Sensor (VSS) connected to the transmission).
* Vacuum Servo: The heart of the system is a vacuum servo. The ECU, based on the desired speed and the actual speed from the VSS, uses electric solenoids to control the vacuum applied to the servo. This servo is mechanically connected to the throttle body.
* Maintaining Speed: If the vehicle speed drops below the set speed, the ECU activates the servo, applying vacuum to open the throttle slightly. This increases engine speed, thus accelerating the vehicle back to the set speed. If the vehicle exceeds the set speed, the vacuum is reduced or removed, causing the throttle to close slightly, decelerating the vehicle.
* Other Components: Other components, such as a brake switch (disengaging cruise when the brake pedal is pressed) and a clutch switch (for automatic transmissions, often disengaging it when the clutch is depressed) are also involved in the system's safety and functionality.
Why it might *not* work:
If your 1994 Ford Aerostar's cruise control isn't functioning, several things could be wrong:
* Vacuum Leaks: A major culprit in older cruise control systems. Leaks in the vacuum lines can prevent the servo from operating correctly.
* Vacuum Servo Failure: The servo itself can wear out or malfunction.
* Electrical Problems: Faulty switches, wiring harnesses, the ECU itself, or the VSS can all disrupt the system. A blown fuse is also possible.
* Throttle Cable Issues: While not directly part of the cruise control, a sticky or damaged throttle cable can interfere with the system's ability to precisely control speed.
To troubleshoot, you'd need to systematically check each component. A repair manual specific to the 1994 Ford Aerostar would be invaluable, detailing the system's wiring diagram and providing troubleshooting guidance. You might also consider consulting a qualified mechanic, as diagnosing cruise control issues can be complex.
