Cadillac: dashboard A/C controls, vacuum source, vacuum line

Question
I plan to purchase a 1991 Fleetword that only blows the A/C to the defroster (winsheild) vent.  I assume that it is a nest of contacts and relays behind the dashboard and I don't want some young schmuck at the dealership, who's never even seem a 1991 FleetHog going in there and messing with it.  If I could get a schematic.  I have a degree in electronics.  What do you think?

Answer
This air going to the defroster vents is the DEFAULT position whenever you lose the vacuum source from the engine, thru the firewall and into the dash components. Look around the firewall for a vacuum line and find where it attaches to it's vacuum source in the engine compartment.


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