2003 Chevy Astro heating

With the Heater relay not energized they 20 amp Heater/ac fuse supplies Power for Low and Medium speed windings, High settings Energizes the heater blower relay (Via org wire on blower motor resistor and relay pack) and supplies power from the 30 amp Maxi
fuse. Be sure to check Both fuses. I am not sure what type damper controls are on that year but if they is a vacuum ported switch and bellow type actuators check to see if master line (from intake manifold ) is connected and supplying vacuum to the switch. The lines are very small and resemble 12 gauge wire but they are plastic tubes.