Vacuum operation of control
 

My g30 only has a defrost outlet working..no center vents..any helpful time saving tips before removing the dash? Thanks

Haha Mr Wizard. Like the name.
Probably a rotted out vacuum line. Have a gander under the hood.

When HVAC in a car looses vacuum, it will revert to defrost.

On my '02 1500 Express I found the soft line from the "T"
to the reservoir ball had fallen off due to the end splitting.
This is accessible from the hood, right next to the battery.

Dunno how or whether newer / older are much different -
G30, what year & motor?

At that same "T" you could check motor vacuum and if
none, check the other end of the "hard" (plastic) line to
the manifold vacuum port; if attached there and no far
end vacuum, suspect plastic line cracking and replace
with a full run of rubber vac hose.