Can someone explain to me how these work...

when the truck is turned on,,what keeps the actuators from Engaging..Is the Iar Pushed into the Vacuum or is it sucked out to keep them from Engaging..I am having a Problem with my 2004 Ford F150 FX4 and my 4x4 is sticking..my mechanic gave me a temporary fix to remove all the Fuses pertaining to the 4x4..and it still seems engaged..should i put air in the Actuator Hub to disengage them or suck the Air Out to disengage...Much help would be greatly appreciated...need to travel about 500 kms before i can get my truck in the garage and fixed up...