Why does my AC unit smell musty?

Eco3 Environmental Uncategorized Why does my AC unit smell musty?

Mold requires three things in order to grow: 1. Organic material. 2. Moisture (water) 3. Oxygen  Over time the AC unit will collect dust, dander, dirt and other material that may contain organic material inside the housing. So, you now have 1 of the 3 needed. There is Oxygen in the air. Now we have 2 of the 3. The AC unit is one big condenser which produces moisture. Now we have 3 of the 3 needed. So, it is just a matter of time before mold and bacteria are growing in you AC unit. Although the means of contamination is different, this is common with all AC systems, including residential and commercial HVAC systems.


Window-Mount – We offer services to address mold in these units, however the prices of new units are so inexpensive, unless you had two units to treat, it may not be worth it. 

HVAC – Unit and duct cleaning by a certified professional is advised. If you cannot find one, we can recommend one for you. Just send us an email. Install an UV/Ozone purification system. Email us for more information.



1. Make sure the drain hole is not clogged. 

2. Follow the manufacturers’ recommendations for mounting the unit. If the unit is not at the proper angle, the water may not flow out as designed. This does not mean you should angle the unit. PLEASE, follow the manufacturers mounting procedures. 

3. Try to keep the unit clean by regularly cleaning or replacing the filters. 

4. Make sure the unit is completely dry before storing it. Also make sure the unit is covered during storage so dirt does not enter the unit. 

 HVAC Systems 

1. Replace the filters as recommended by the manufacturer. 

2. Frequent cleaning of the ducts. 

3. We offer the installation of UV and Ozone air purification units. These are low cost, low maintenance units. 

4. Proper insulation to prevent condensation. 5. Proper drainage. 

AC Unit Placement Issues

Basement Windows – The closer to the ground an AC unit is placed, the more it is likely to become a breeding ground for mold and bacteria. A low mounted unit is subjected to dirtier air and debris blown around by the wind. Also, insects are more likely to make it a home. 

Dark Side – AC units that do not get sunlight are prone to develop mold/growth issues. We have also encountered moss growing on them. 

Street Mount – If an AC unit is mounted near a busy street or traffic area, indoor air quality issues may occur. This is more common with diesel engines since the diesel exhaust is heavy and tends to linger. 

Legionnaires’ Disease

Not just mold can form in you AC unit, bacteria can as well. Bacteria can be just as or more harmful than mold. Regardless, you don’t want one, either or both! Unfortunately, the biofilm coating found in most water containers harbor mold, bacteria and other microorganisms forming dangerous dynamic communities.

CDC States:

What is Legionnaires’ disease? 

Legionnaires’ disease (LEE-juh-nares) is caused by a type of bacteria called Legionella. The bacteria got its name in 1976, when many people who went to a Philadelphia convention of the American Legion suffered from an outbreak of this disease, a type of pneumonia (lung infection). Although this type of bacteria was around before1976, more illness from Legionnaires’ disease is being detected now. This is because we are now looking for this disease whenever a patient has pneumonia. Each year, between 8,000 and 18,000 people are hospitalized with Legionnaires’ disease in the U.S. However, many infections are not diagnosed or reported, so this number may be higher. More illness is usually found in the summer and early fall, but it can happen any time of year. 

What are the symptoms of Legionnaires’ disease?  

Legionnaires’ disease can have symptoms like many other forms of pneumonia, so it can be hard to diagnose at first. Signs of the disease can include: a high fever, chills, and a cough. Some people may also suffer from muscle aches and headaches. Chest X-rays are needed to find the pneumonia caused by the bacteria, and other tests can be done on sputum (phlegm), as well as blood or urine to find evidence of the bacteria in the body. These symptoms usually begin 2 to 14 days after being exposed to the bacteria. A milder infection caused by the same type of Legionella bacteria is called Pontiac Fever. The symptoms of Pontiac Fever usually last for 2 to 5 days and may also include fever, headaches, and muscle aches; however, there is no pneumonia. Symptoms go away on their own without treatment and without causing further problems. Pontiac Fever and Legionnaires’ disease may also be called “Legionellosis” (LEE-juh-nuh-low-sis) separately or together.  

 How serious is it? What is the treatment? 

Legionnaires’ disease can be very serious and can cause death in up to 5% to 30% of cases. Most cases can be treated successfully with antibiotics [drugs that kill bacteria in the body], and healthy people usually recover from infection. 

OSHA Quotes: 

It is estimated that in the United States there are between 10,000 and 50,000 cases of Legionnaires’ disease each year. Legionnaires’ disease is a bacterial disease commonly associated with water-based aerosols that have originated from warm water sources. It is often associated with poorly maintained cooling towers and potable water systems.

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