I was driving one day then suddenly a thumping noise came from under the hood. I pulled over and found the clutch to the AC was sitting on top of the radiator housing. The pulley is still on and the bolt that holds the clutch s gone. Should I replace the clutch or the whole AC unit to fix it?

 

you can just replace the clutch and front seal if you wish

 

Just buy a bolt and put it back on, you have to get a washer to fit in between the shaft and clutch, use locktite on the bolt when your putting it back on. If your clutch bearing is going you can get one from autozone for the ac clutch hub.