I'm not getting any air flow thru the dash vents. It doesn't matter if it's A/C or heat, or the blower speed.('84 El Camino) any suggestions.

check too see that the vacuum hose under the the hood hasn't become disconnected from the vacuum ball or a split hose

Yeah, it does sound like a vacuum leak, or a hose maybe came off someplace. These cars are OLD, and replacing all those old vacuum hoses is a good idea.......