“My air conditioner smells musty!” Don’t feel weird about calling your local HVAC technician because of unpleasant smells coming from your vents. An odor can be used to help diagnose a problem with your HVAC unit.

Common Questions About Smelly Air Ducts and HVAC Units

Before we answer common questions about your smelly air conditioner, we would like to highlight one unpleasant smell that should never be ignored – natural gas. Natural gas is often described as smelling like rotten eggs.

  • If you notice a strange smell that reminds you of sulfur, call 911 immediately and leave the premises.
  • Do not turn on (or off) lights or appliances.
  • Do not attempt to find the source of the smell yourself.
  • Do not open your windows.

While a musty-smelling AC unit might be cause for concern, it is not an emergency. However, that doesn’t mean you should ignore the smell because it indicates that your AC unit is not functioning correctly.

Why does my air conditioner smell musty?

Generally, musty smells from an air conditioner unit are caused by accumulating water in drain pans, drip lines, or ducts. However, it can also be caused by a dirty air filter.

Possible Reason #1: Drain Pan is Full

Your AC unit removes moisture from the air in your home. These water droplets fall into the drain or drip pan. After some time, a drain pan may accumulate mildew or mold. The drip pan, located under your system’s evaporator coils, can be replaced to remove the smell.

Possible Reason #2: Blocked Condensate Drain Line

The unit’s condensate line is a small pipe located next to the condenser unit outside your home. The condensate line drains water from the drip pan. However, mold, mildew, and sludge sometimes build up in the line and cause it to clog. Once the blockage is removed, the smell may disappear.

Possible Reason #3: Excess Moisture In Ducts 

If there is a musty smell coming from your AC unit, there’s a chance that you have mold or mildew in your ductwork. This may cause a musty AC smell to come out of your vents. To remove the musty smell coming from your ductwork, schedule routine cleaning.

Possible Reason #4: Blocked Air Filter Caused Your Condenser Coil to Freeze

A dirty air filter may cause the water droplets to build upon the evaporator coils. These water drops will freeze as the AC unit’s refrigerant cools the air. Your professional HVAC technician must let the condenser coil thaw and change the filters to restore maximum airflow.

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Can a musty AC make you sick?

Mold exposure can cause upper respiratory health issues. If your air conditioner smells bad, it is a good idea to find the cause and remedy the situation.

How do I get the musty smell out of my air conditioner?

If your air conditioner persistently smells musty, you may need the help of a professional. HOP Energy HVAC technicians can help.

You may associate HOP Energy with our heating oil delivery service. However, we also offer HVAC service, maintenance, and installation throughout the Northeast. So the next time your AC smells bad, fill out the contact form on the HOP Energy website. We will find the reason for the musty odor, fix the problem, and give you ideas to improve your home’s indoor air quality.

What We Have Learned About Musty-Smelling Air Conditioners

  • Your air conditioner unit should not smell musty. If it does, there’s something wrong with your air conditioning system.
  • The musty smell might be caused by a full drain pan, a blocked drain line, excess moisture in your air vents, or a blocked air filter. All these issues can be fixed by a company offering AC repair services.
  • Mold spores can be harmful to humans and pets.
  • HOP Energy offers AC repair and maintenance.

Contact us today