This is the 3889th most frequent Korean word.
에어컨을
"에어컨을" means "air conditioner" (object form).
The word '에어컨을' (air conditioner) is used as the object of the verb '사용합니다' (use), indicating the device being utilized.
여름에는 에어컨을 자주 사용합니다.
In summer, the air conditioner is used frequently.
Here '에어컨을' is the medium or means by which the action of lowering the room temperature is achieved, modifying the verb '이용했어요' (utilized).
에어컨을 이용해서 방 온도를 낮췄어요.
Using the air conditioner, the room temperature was lowered.
In this case, '에어컨을' specifies the item that was fixed and subsequently broke, linked to the verbs '고쳤는데 / 고장이 났어요' (repaired / broke down).