What Are the Causes of Smelly Air From Air Conditioners?

Dirty Filter

• The air conditioner filter can become clogged up with all sorts of dirt, dust and debris, leading to unusual smells when the air conditioner is running. If the unit has not been run for a while, or if the filters have not been changed for some time, the odor can be especially bad. The filter captures not only dirt and debris, but can hold odors that have traveled through the vent system, such as cooking fumes or those from outdoor animals.

Mold

• Anywhere there is a constant source of water, there is likely to be mold. This is true in air conditioning units. Over time, mold can build up on all parts of the unit, including the filter and coils. This mold can cause the air conditioner to emit a musty, moldy smell. The smell will circulate through the house and back through the unit, intensifying the problem. If the unit smells musty, mold is a likely culprit.

Bacteria

• Like mold, bacteria thrives in moist conditions. It can grow rapidly in the water and on all the moist surfaces of the air conditioning unit. Eventually, the bacteria will cause the air traveling through the unit to smell bad. It may smell musty, similar to mold, or it may smell sour or rotten.

Cleaning

• The solution to all air conditioner odors, regardless of the cause, is cleaning. Air filters should be replaced at least once per year, or more often in dusty and dirty conditions, or if odors re-occur. The filter should also be cleaned about every two weeks. The entire unit should be also be cleaned with a product that kills mold and bacteria. Open the front of the unit and spray the coils, condenser and inside of the air conditioner with the cleaner. Repeat the cleaning every two to three months to prevent future mold and bacteria problems.