Fan blower works on manual not air coming out of vents

Fan blower is working no air is coming out

So your can hear it running but no air is moving? Try opening the door to the blower compartment and tricking the safety switch, do you see/hear/feel a great deal of air moving in the compartment?

The fan blower is working, you can here it running. The air just stopped coming out of the vents.

Try the door trick. You could hear a motor running but that does not mean the squirrel cage is spinning

Any Duct Valves? Like above, Does Air suck in on the return air. Check registers closest to the unit for air.

Have you gone to furnace and took a close-up look-see and positive the blower is working? Since you didn`t say wheather you had a gas, electric,oil furnace its hard to guess what problem might be,, check it out and give us more info,so we can help you

If you know that the fan motor is working (and squirrl cage is moving)and you have no air at the registers than you have to start looking for a major supply duct leak or your coil (if a heat pump/AC) is very dirty.

Can you supply some more info on the type of unit - package or split system (http://www.thermal-medics.com/a-c-image-glossary/)? If you are running in a/c mode and the coil is super dirty than ice will be forming on the evap coil. here are some pics to show you one I saw not to long ago (http://www.thermal-medics.com/a-c-image-glossary/)- very dirty coil and no airflow in home. Scroll to bottom for that pic.