Memphis I think you mean the AC compressor clutch, which is also the pulley driven by the drive belts. It's electromagnetic and if it goes bad, just rotates freely (but appears to be static even with the belts running around it) without cold air going into the cabin even with the AC on.

You can tell if the clutch is bad. With the engine running look at the AC clutch. If the AC is on, the clutch should also be rotating. If it is off, it should remain static. So if the AC is "on" but the clutch remains static, then the clutch is bad.