If your window unit air conditioner isn't working as well as it used to, it may just need a deep cleaning. Air conditioners that aren't cooling the room very well may need more refrigerant, but a buildup of dust and other debris on the appliance's filter, coils and other hardware could also be the culprit. Not only is a dirty air conditioner inefficient, but it can also be dangerous to your health, as it could be circulating mold spores into your home. A few times a year, take your window unit apart and inspect it to keep it running like new.