The fresh air intake air cleaner is on top of the Control Valve. The vacuum line connects to the silver nipple located on the bottom.
Here's how it works. When you step on the brake pedal it puts hydraulic pressure on the control valve which opens the fresh air intake allowing 14 psi of atmospheric air pressure to push on the back side of the Hydrovac piston. The piston then push's on the Hydrovac's Master Cylinder which increases the hydraulic brake line pressure by about 800-1000 psi. The engine vacuum removes the 14 psi air pressure from the front side of the piston via the vacuum line allowing it to work.
Make sure you have the vacuum line connected to the silver nipple. Is this where you attached your test pump? The vacuum side should be air tight.
Mike B
