AC stopped working

I was driving to work I came to the entry gate and stopped. When I start it again on acceleration it sounded like metal on metal. when I let off the throttle it would stop. every time I accelerated it would sound like metal on metal grinding. That happened about five times driving around the parking lot and then it stopped making that noise all together. I didn't know at the time what it was but then later I found out my AC wasn't working so apparently it was my AC. I have a feeling the compressor went out but I'm really not a mechanic.