Check if the Air-filter is blocked by dust. If there is a lot of dust on the air filter, then the cooling efficiency of the air-conditioner might decrease. Constantly clean the Air-filter with water to improve the efficiency of the air-conditioner. Check if the outdoor unit is covered or installed near an obstacle. Take the cover off and take the obstacle away. If the doors and windows are open, it may cause bad cooling performance. Close the door and windows. Check if the pipe length that connects indoor and outdoor unit is too long, the cooling performance of the air conditioner decreases if the pipe length exceeds maximum allowable length.