90' XJ Heat/AC schematics

[chrs93]

I was hoping someone could explain to me the heat/ac controls and how they work before I tear into mine. When I switch from one setting to another on my controls the air flow does not change positions. meaning from defrost to vent, etc. I was unsure if this was a vacuum system that switches the flow if it was mechanical or electrical. I have no background info on it. Any help is appreciated.

[4.3LXJ]

Those controls for the vents are vacuum operated. Defrost is default. You probably need to establish vacuum to them. The most common thing is a cracked reservoir which is located behind the front bumper