The little unit you are refering to is the air control valve.
When the valve is switched on, atmospheric air is sent to the vent pipes on the front and back of the supercharger. This makes the front and rear bearings near atmospheric pressure, and thus stops the grease and oil from leaking due to pressure fluctuations inside the supercharger.
When it's off there is just a bridge between the two vent pipes. I believe there is some sort of load/rpm condition where the ecu decides to switch it on.
With regards with the vacuum lines I have a tech article on the ABV modification that might help a little:
Mon, 01 September 2003 14:39
