My House Air Conditioner Smells Like Sewage

Clogged Condensate Drain

• A clogged condensate drain can cause a sewage smell. As indoor air is passed over cold Freon coils to be cooled, the water vapor from the air clings to the coils, which makes the coils "sweat" in much the same way a glass of cold water sweats in a hot room. This sweat drips down into a condensate pan and is drained away from the unit. If the condensate pan is not draining properly, there can be standing water that can smell much like a sewer. Check that your condensate drain is not clogged and your air conditioner is draining normally.

Problem at the Intake

• Your air conditioner pulls in air from inside your home, cools it and recirculates it through your home. Examine your intake points, which are the grills that contain the air conditioner filters. If the filters are clogged, wet or just generally dirty, you can be getting a sewage smell from them. Additionally, verify that a sewage smell unrelated to the air conditioner, but in the room with the intake, is not simply being circulated throughout your home.

Moisture in the Duct Work

• If your air conditioner has not been serviced lately, an improperly functioning system may have allowed water vapor to escape into your air conditioner ducts. This water coats the inside of the ductwork and forms a breeding ground for mold and mildew. Over time, the mold and mildew decomposing can cause a sewer smell to emanate from the air conditioner vents. Pull off a duct and examine it for signs of water damage or mold growth.

Trap Malfunction in the Sewer Condensate Drain

• Some air conditioners are installed in such a way that their condensate drain dumps directly into the sewer line for the house. If this drain is installed without a trap or a small piece of elbow pipe that is always filled with water, sewer gas can back up through the condensate drain and make its way into your circulated air. Examine the drain hookup, and ensure there is a trap installed and that it is functioning properly.