Translation:Please turn off the air conditioner.
My wild guess would be to indicate the change in status, in this case going from A/C on to A/C off. But whoever knows better feel free to correct me.
Actually, I think the "了" normally would not be used in this instance. "请把空调关起来" sounds more apt.
Please turn off the air con that's the correct answer I got , airco sure but air con is also correct?