A/C not flowing through the vents on 1992 Chevrolet S10

I have replace all 3 switches in the control panel, the blower motor resistor on the firewall, have checked every vaccum hose that i can see. I only get air flow to the floor and the blower only works on high. How do i get the air to flow through the vents and should i replace the blower motor?

Asked by for the 1992 Chevrolet S10