[Issues]

So I was driving to school one day, and was sitting at a red light when I thought to myself, what would happen to my RPM's if I turned my air conditioner on while I'm just sitting here. I hypothesized that they would go up because i figured the air conditioner would provide a greater load on the engine so it would need to spin faster to keep up. An amazing thing (to me) happened, they went down. I tested it out a few times, and sure enough if I turned the air conditioning on all the way the needle would pop down and if i turned it it off, it would pop back up. Why is it like this?