Vacuum overview
The accelerator pedal (AP) servo is vacuum assisted. The vacuum is created by a vacuum pump. Air can be allowed into the servo via the regulator, which is also located in the pump housing. As an extra safety measure pedal switches have valves which allow air into the system when the pedals are used.
Vacuum pump and regulator
If vehicle speed drops the vacuum pump is turned on to increase the vacuum in the system. If vehicle speed increases the regulator allows air into the system to reduce the vacuum. The vacuum pump is driven by an electric motor which is switched on when the SET+ button is pressed and the control module relay is closed. The relay switches the power supply to the pump motor. The motor drives the pump until the vacuum servo has a sufficient vacuum to maintain the selected speed. This speed is transmitted to the control module via a signal from the speedometer. The control module then opens vacuum pump grounding.
When extra power is required, when driving up a hill for example, the vacuum pump is switched on again in order to increase the system vacuum until the selected speed is achieved. When driving downhill the regulator vacuum valve is opened to allow air into the system, reducing the vacuum to the vacuum servo and reducing throttle opening.
Vacuum servo
This is located above the accelerator pedal (AP) and consists of a housing containing a diaphragm to which a control rod is connected. When a vacuum is introduced behind the diaphragm it moves in that direction pulling the control rod with it. This in turn acts on the accelerator pedal (AP).
Pedal valves (vacuum valves)
These are integrated with the pedal valves.
Each vacuum valve is operated via a spring-loaded piston. The valve is self-adjusting.
Normally, when the pedal is released, the spring is compressed and the vacuum valve is closed.
If the clutch or brake pedals are depressed, the spring pushes the piston back.
The vacuum valve opens, allowing in air and disengaging cruise control.