ac engine problems

Another thing that my car does is when you go to turn on the car and then you turn on the ac...well the ac doesnt work but when i tried it before i knew it worked and then i found out it didnt i went to turn it off and well the engine also died with me turning off the ac. What could of caused this to happen? Another thing is when the AC did work and i turned off the AC the engine would sometime like want to die and sometimes it would die when i turned the AC off what could of caused that?