Stinky Air Conditioner Smell

Clogged Drain

• Air conditioners not only blow cool air into a room, they also remove dust and moisture from the air. As the unit dehumidifies the room, the air moisture is condensed inside the air conditioner, and the liquid drips out of the unit's drain hole or pipe. If this drain outlet clogs up, the liquid pools inside the unit, collecting bacteria and causing mold. Regularly clean the unit's drain system and drain hole, at least once every month, to prevent this from occurring.

Dirty Filters

• The filters inside both window air conditioners and central air conditioners trap particles inside the air entering the unit. This air can be filled with odors from cigarette smoke, smog, pets, pollen and other sources. If caught by the filter and left there, smells will occur. Remove and clean the filter with water and detergent when a layer of dust accumulates on the filter screen or replace the filter with a clean one.

Outside Odors

• A window air conditioner has vents on the side of the unit that allow outside air into the appliance. If this outside air is polluted or smelly, it transfers into the room. This problem is not the fault of the air conditioner, because it's simply operating as it's designed to operate. If you're unable to remove the odors outside, a solution is to relocate the air conditioner to a different room window, maybe on a different side of the house.

Dirty Interior

• Especially after the air conditioner is left inactive for a long period of time, dirt accumulates on the fins of the evaporator coils behind the unit's grill. Wet dirt and debris can stick to the coils because of the moisture being removed from the indoor air. When this happens--with mildew and mold developing--the smell passes into the room when the air conditioner is finally turned on. Unplug the unit, remove the grill and use a vacuum with a soft brush attachment to clean the coils and fins.