1994 Cadillac Fleetwood heater

Check the vacuum source connection. It will a small plastic tube connected to either to the intake manifold or to a junction on the firewall. The tube is usually black or red. I vacuum source is good, check under the dash to see if the vacuum dampers are moving as you turn the selector switch from floor heat to AC, and from floor heat to defrost. If nothing moves, check for vacuum at the selector switch. If yes, change the switch.