There are few reasons why your AC may be smelly. Determining the cause can help you decide what needs to be done.

AC Odor Causes

Foul odors tend to stem from one of three locations in the AC: the filter, the ducts, or the evaporator coil. Filter and duct odors are caused by a collection of dirt, dust, mold spores, and bacteria. The smell is usually that of damp and mildew, although there may also be a sour smell if bacteria are present. You will primarily smell filter and duct issues when the AC is running, regardless of the season.

Evaporator coil odors can be likened to that of smelly socks or dirty laundry. You are more likely to experience this issue in spring or fall, when outdoor temperatures are much cooler and there is more moisture in the air. Moisture collects on the coil, which causes dirt and debris to stick to it. Mold and bacteria then begin to grow, leading to the foul odor.

Odor Concerns

Smelly odors can be more than a nuisance, though. If mold and bacteria are growing inside the AC unit, then you can be sure that the spores are spreading throughout your home each time the AC is running. Those spores can lead to headaches and respiratory issues in some people. If anyone in your home has a mold allergy, then they can be quite uncomfortable when the AC is running. Mold and bacteria tend to grow when dirt is present as well. This means that pollen, pet dander, and dust mites can also be collecting in the AC or ducts.

Dirty coils, ducts, and filters are also problematic for the AC. The dirt can restrict airflow through the system, which can lead to an overworked and overheated blower motor. Dirty coils are also less effective at creating cool air, so the system may not work as well as it should.

Repairs and Remedies

Repairing foul odors means cleaning out and replacing those parts where dust, mold, and bacteria are collecting. Regular filter changes, as well as complete cleaning of the filter housing, is an important task. You may also need to schedule a full duct cleaning if the odors are originating from within the duct work.

For issues with the evaporator coil, a full cleaning is in order. Of course, some condensation is still normal even on a clean coil, so the drain system must also be inspected. You need to have the drainage system inspected. Blocked drains and lines may need to be cleaned and replaced so that bacteria and mold can't grow.

Contact an air conditioning contractor in your area if you need more help with a smelly AC system.