climate control problem Help

My 4 wheel drive stopped working somthing to do with the vacuum I was told to check the climate control and see if it was sticking on defrost? well turns out that I was using my air conditioner and it switched from blowing out the panel vents to blowing from the defrost then a couple seconds later it went back to the panel by itself, does anyone know what my trouble is I am sure this is what is wrong with my 4x4 also!

Definately be your vaccuum pump. Located under the hood on the passenger side. Very easy to get at and easier to change.