Macbook doens't go to sleep when lid is closed

Hello,

Since 3 moths i have a problem with my macbook. If it is connected to AC power it doesn't go to sleep when i close the lid. If I plug the AC it out, it does go to sleep. And whenever it is in sleeping mode and i plug in my AC, it goes back on. The health of my battery is running back very fast and i would like to fix the problem before i have to buy a new battery.

I tried resetting my power settings but that didnt help. I didn't change anything in my macbook when this startet. Does anybody have an idea?

Thanks in advace,

Robin