Just reactivated my "death star " system a while ago. It serves as a vacuum reservoir for the recirc flap operation. When you go into A/C mode an electric solenoid activates a valve allowing a vacuum motor to close outside air from being inducted into the vehicle. There is (should be) a vacuum check valve in the hose to the death star also. The check valve keeps the system from losing vacuum during decelleration thus preventing hot outside air from being occasionally inducted into the cabin. There is a small hose from the death star that runs through the firewall, under the steering column (NA spec) and up into a solenoid valve that's just barely reachable on the (NA spec) drivers side of the dash core conflagration.
All this really only matters if you live in a seriously hot, humid, place. Then the dumping of outside air into the cabin defeats the A/C... which is rather marginal anyway. If you don't need it, then plug the hose at the plenum and enjoy a constant flow of fresh outside air.
May the Force be with you... :roll: