If it is the part of the room on the far end, the air from the air conditioner simply isn't making it that far and whatever caused you to turn on the air conditioner in the first place is warming that part of the room. 2,4000 BTU is probably enough to cool that space, unless it is a 1-story, with a roof over it, but no air conditioner can effectively throw cold air 20 meters. That's what ductwork is for.