heater controls not working.

88 lx 2.3 I just bought I finally got the blower motor working and the heat and cooling switch/knob works. but i cant get the face/floor,floor,floor/defrost switch/knob to do nothing I know it works off vaccum but from where? cause I do not have any vacc leaks? unless maybe someone has plugged it off i dont really know. basically where does the switch get its vaccum?