Indeed --see recent thread on same subject - disconnecting the hose makes sure no partial vacuum is applied, because the solenoid valve www.geocities.com/lmp4203/kiasport/vacsol.jpg
leaks and leaves the hub in attempt to engage, but is not able to do so.
NOtice that the condition of the hub after that is quetionnable. SO , first of all, if you reinstall the vacuum hoses, take the solenoid valve out, clean, make it operate with a 12v supply (battery charger) several dozen times, circulate some solvent through the ports to clean dust particles from the valve seat..then try again to connect it and see if all works well..that is positive engagement when on 4wd, and complete disengage and no grinding noise when on 2wd.
I doubt in fact the vacuum hubs have survived...as they are the most common source of problems and eventually need replacement with WARN manual or automechanical.
Come back to tell the results.
(instructions here for replacement with automechanical)
www.geocities.com/lmp4203/kiasport/hubinstall.pdf

By the way, for the benifit or readers, it is best to keep this topic on this thread.