Technical parts question For a 1986 Chevy caprice 305 4 bbl?

I had to go and get one of my older books to get your answer. This is from a 1992 Emission Control Application Guide that covers your model year. Requirements are PCV, TAC, EVAP, TWC, FR, BP/EGR, SPK, AIS, O2, CEC, EFE. The one that is for TAC, represents thermostatic air cleaner and the switch that you make mention of is the vacuum control switch for the TAC. You air cleaner has a heat riser pipe that comes from the exhaust manifold to the air cleaner. This provides warm air for cold morning starts and cold weather conditions. The purpose is to prevent icing of the venturi in the carburetor. Hope this helps. It is also an emissions requirement for smog testing.