No air blowing to floor

Hi all, My 98 blazer 4X4 is not blowing air to the floor. It will come out the dash vents and defroster vents. I have read to check the ball under the hood I found I do not have one under the hood so I guess it's under the dash. My question is where under the dash it is and what it looks like? Does anyone have any pics of what i will be looking at when I rip the dash apart? Could it be as simple as a bad switch? I have somewhat ripped the dash apart but have no idea what I am looking for and can't seem to find anything that looks like a ball.

Any help will be great
Thanks

The vacuum tank is flush bolted into the left front fender. It's behind the ABS brake pressure modulator valve. Has one small vacuum hose going to it. If the modes don't switch, usually it's because of no vacuum to the switch.

They do switch from dash vent to defrost vents. But when I put it on floor it just comes out the dash vents..