4wd will not work

I can't figure it out. I have a 93 s15 jimmy with push button 4wd. When I press the button, nothing happens, no blinking lights, no clicking. It doesn't even try. If I am in revearse and push it, hi and lo blink, clicking by glove box, but still no 4wd. I changed the vacuum switch at the transfer case. No help. Found a hole in vacuum tube at actuator under battery. Replaced it and it worked fine. A few hours later, started it, and it is not working again. Doing the same thing. Anybody have any ideas??????