What is wrong if the air conditioner is running but no air is circulating through the front vents?

Check the vacuum hose under the hood. May have a leak or have been disconnected.

Also check -

The blower - this includes its motor, fan and associated components/wiring. Next to check is the coil (this looks like a small radiator) through which the blower moves air is clogged. Check if the vents themselves are clogged.