After tracking down the vacuum problem I was having with my ac vents not working I discovered the problem was the vacuum line that runs along the right hand side fender up underneith the battery, down by the horn, and into a black box. What is this black "box" what is it for and what does it do. For the time being I just capped of the port on the little three way "manifold" up by the firewall where the vacuum line of the intake meets up with the line in question and the one that goes thru the firewall.

 

I suppose that I might also add that the car in question is my 94 Z28.

 

It goes to the vacuum tank. It stores vaccum to enable the HVAC mode switch on the dash to correctly operate during temporary low vacuum conditions.

 

Thanks.