I can hear my truck's air conditioner blower running, but there's no air flow from the vents?

I can hear my truck's air conditioner blower running, but there's no air flow from the vents? - 1

Added (1). It's an 2003 Ford Ranger and the problem happened suddenly.

Your freon leaked out.
You need to fix the leak and recharge the system.

Is it coming out of the defrost vents, or floor vents? Sounds like a vent door problem.

You have hoses that runs the cool air (coolant) out of your vents. You may have to buy a can of coolant, with a hose and gauge that is attached, hook the hose up and fill your hoses. Either that or your connection to the vents is ******. Your vents stretch all the way to the compressor, so both vents probably arnt attached to the AC unit at all. Reattach the vents. Like pilsner said it could be a problem with your vent doors

It's possible a shopping bag got sucked up into the blower motor squirrel cage.