What is Causing That Musty Odor in Your HVAC System?

Have a better understanding of HVAC systems and the causes of sour odor in drain lines and air ducts with experts at Sandium.

Updated on Jan 22, 2024
5 min read
What is Causing That Musty Odor in Your HVAC System?

Is the air leaving the vents in your home stinking whenever your air conditioner turns on? Are you tired of the musty odor in your home? In most cases, the musty smell is from mold or mildew. And, the bad news is that your HVAC system is probably spreading mold spores throughout your Northern California home. This can be harmful to your family’s health, especially if someone has allergy issues.

These are a few sources of musty odor in an air conditioner.

1. Dirty Evaporator Coil

You know this is the problem if the evaporator coil gets frozen or iced up. You may notice weak airflow from the supply vents as well. Evaporator coil is the part that cools the air. If it gets dirty, the HVAC system can quickly turn into a breeding ground for mold and mildew. This is because mold likes food, moisture, darkness, and warm temperature.

The evaporator coil provides 3 out of the 4 elements naturally. It is located in a dark area, is warm and has moisture forming on it. If the coil gets dirty, mold get the food it needs in the form of dust or dirt. You can avoid this by changing the air filters regularly. You can always solve this problem by having a professional clean the evaporator coil.

Generally, the evaporator coil is cleaned as part of annual maintenance. You can use a UV germicidal lamp as well for preventing mold from growing on the evaporator coil.

2. Condensate Drain Line is Clogged

You probably have a problem with the condensate drain line if the air conditioner shuts down after running for some time. This is because water is probably flowing over the condensate pan and triggering an in-built emergency shut off. You should look for signs of water pooling around the air conditioner.

Condensation forms on the evaporator coil and drops into a drain pan. This is exited from the unit through a drain line. However, in case the drain line gets blocked from dirt or dust, water tends to back up into the drain pan. Mold will get everything it needs to grow in the form of darkness, moisture, food, and warm temperature. You can always use DIY tips for cleaning the condensate drain line. You can also hire a professional to get the job done for you.

3. Air Ducts are Leaky

Leaky air ducts can be a source of musty odor as well. There could be a leak if the air conditioner runs for a long time but doesn’t really make a difference to the indoor temperature. You would notice that the indoor air gets dusty quickly as well. Another sign that you have a leaky air duct is that the house is humid even with the air conditioner running.

Leaky or disconnected air ducts draw in surrounding air. This is usually filled with dust, dirt, and mold spores. This air can cause the evaporator coil to get dirty. It can also make mold grow inside the ductwork. You should have a professional look at the ducting to ensure everything is alright. You can also use a one-two punch of duct sealing for eliminating leaks. Make sure you clean the ductwork for removing dust, mildew, and mold.

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