My question is: how is the heat and vent selection controlled on a 1996 Suburban?
Is it electric or vacuum?

My vent is stuck in defrost and there is no heat. (I relied on the rear heat for the tail end of this past winter.)
AC is shot too, but it has been for 4 years.(bad compressor) Heat quit this past winter.

I was thinking of switching out the HVAC controls, but thought I would throw this out to the group before I buy a replacement.