A musty AC unit is usually one that isn’t properly maintained or that is malfunctioning in some way.  HVAC odors are almost always associated with excess moisture occurring somewhere it shouldn’t be in the system. The ensuing growth of mold and mildew is what often causes the disagreeable scent.

Moving moisture is part of the cooling process. Air conditioners continuously extract moisture from the air at the indoor evaporator coil. On a hot summer day, gallons pass through the drip pan below the AC air handler and then into a drain line that’s usually connected to the home-plumbing drain. Humidity present in the indoor air can also affect other HVAC components such as the air filter, triggering moisture issues, including odors, and a musty AC system.

Below are some of the ways that moisture generated by the cooling process may result in a musty AC system.

• Mold and mildew inside the AC drip pan. Fungus may spawn inside the air-handler drip pan. This can usually be eliminated by an HVAC service technician who will disinfect the pan and add fungicide tablets to the pan to inhibit further mold and mildew growth.
• Water spillage around the indoor unit. Ice formation on the indoor evaporator coil can leak water outside the drip pan when it melts, causing musty odors. Chronic coil icing indicates a system malfunction such as a low refrigerant charge. This should be diagnosed by a qualified HVAC technician.
• Drip-pan overflow. A drip pan that repeatedly overflows — usually the result of a partially clogged drain line causing slow drainage — can provide a continuous source of moisture around the indoor AC component. Contact your HVAC professional to assist with this issue.
• Dirty air filter. In daily usage, an HVAC air filter becomes increasingly permeated by airborne contaminants such as bacteria, mold spores, mildew, and pollen. Meanwhile, excess humidity in the system airflow may also dampen the air filter. This combination can cause the filter to become a source of musty odors. Your HVAC contractor can advise you about the best filter for your home and how often to replace it.
• Mold or Mildew in vents and ductwork.  Mold growth occurs with two components, warm temperature and moisture. A humid climate, poor ventilation, and anything that traps moisture can lead to issues with vents and ductwork. Mold and mildew can give off a musty odor as well as be a health hazard for residents. An HVAC provider is needed to provide a ductwork inspection.

Contact the professionals at Jackson & Sons for solutions to musty AC odors in your home.