Why is my house air conditioner running but no air is coming out of vents?

Check your furnace fan. The air conditioner unit can be running but the air circulation is usually done with the fan on the furnace. If you have a fan switch on the thermostat, check to see if it is in the auto position. If it has the settings on/auto/off, you can switch it to the on position and see if you get any air movement then. If not, you could have a broken belt.