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5 Reasons Why Your Air Conditioner Smells Musty

Air Conditioner Smells Musty

If an unpleasant smell comes from your AC, you have cause for concern! Smells are usually a sign that something has gone wrong inside of your HVAC system. Not to mention a foul odor can be disturbing and embarrassing.  The most likely reasons that your AC smells musty are:

  • Clogged air filters
  • Clogged condensate line
  • Evaporator Coils
  • Excess Moisture
  • Pests
  • Or other causes!

At Cardinal Heating and Cooling, we know how to diagnose where a musty smell is coming from and how to make it go away forever. Call us at (703) 721-8888 or schedule service online to schedule service with us.

The Most Common Causes of Musty Odors

Various components of your HVAC system accumulate dust, debris, and moisture. Thanks to your air filters and drain lines, you usually don’t have to worry about the adverse effects of grime and moisture.

If there is an issue with any of the following, you may be experiencing the results of a smelly buildup of debris and mildew:

Reason One: Your Air Filters are Clogged. 

Not only do your air filters create a barrier against hair and dust, but they also absorb mildew and mold. Foul microorganisms thrive if your filters aren’t changed frequently.

Furthermore, a block will cause dust to accumulate in your ducts. That musty odor could be due to the growth of mildew in your HVAC system or a buildup of dust in the ducts and vents.

Reason Two: Your Condensate Line is Clogged.

If the condensate line has become clogged, there will be nowhere for the moisture produced by an AC unit. 

Clogs can form in a condensate line due to debris, protruding roots/vegetation, or damage.

Reason Three: Dirty or Frozen Evaporator Coils

All the air that flows through your home must pass through the evaporator coils on your indoor AC unit. Like any other AC components, the evaporator coils can also suffer from dirt buildup or too much moisture.

If the condensate line or drain pan cannot release the moisture from the unit, it will cause the coils to freeze. You can tell that your AC evaporator coils have frozen if your AC leaks or blows hot air.

Reason Four: There’s a clog in the drain pump. 

The condensate drain pump is the last place to collect moisture to leave your property. The pump can get clogged by a buildup of gathered debris that is in the water. 

Without this, the AC will not be able to function properly, and there is a risk of mildew and mold growth. 

Ensure to check your drain pump to make sure all of the gathered moisture can exit freely.

Reason Seven: You Have a Pest

When’s the last time you looked in your ducts. Bugs, birds, and rodents can find their way into your HVAC system without being noticed. However, eventually, you will notice the smell that they create. 

Pests will damage your HVAC system if ignored, and some pests can even spread dangerous diseases and other airborne contaminants.

Find Professional AC Repair in Sterling, VA

To stop dangerous particles from impairing the air quality of your house, contact a professional as soon as you notice a strange smell coming from your cooling system.

You can stop musty odors before they ever start growing in your house if you ensure to schedule routine air conditioning repairs.

The HVAC specialists at Cardinal troubleshoot problems with air conditioning repairs in Sterling. Our extensive professional experience and knowledge are something we are proud of.

Call us today or schedule online to receive the best HVAC services near you.


1. How Do I Get Rid of Musty Odors

Now you’re wondering, “what do I do now?”. The short answer is always to call a trusted technician to help you troubleshoot, but you can still take some steps to keep your AC smelling fresh and clean. Here are some steps you can do to maintain your AC fresh and clean:

  1. Before diving inside your HVAC system, turn off the system via the thermostat. Moving and electrical components are dangerous if not handled correctly.
  2. Change your air filters! We recommend changing them every 90 days or even more frequently if you have pets or children.
  3. Check your indoor and outdoor AC units to ensure they’re in working order.
  4. Ensure that your evaporator coils are clean, and if not, we recommend spraying them with a solution of bleach and water.
  5. Check your condensate drain line and pump for damages, clogs, and other instructions for proper draining.
  6. Smells are usually signs of hazardous contaminants, so we do not recommend handling them on your own. Keep yourself safe and your family, and call an HVAC technician near you!

2. Should I worry about the smell?

Sometimes, an AC unit or furnace can emit a smell. At the beginning of the cooling or heating season, your HVAC system may occasionally release a burning odor as it burns off the accumulated dust. 

However, most smells from an HVAC system are signs of trouble. If you smell something rotting, you may have a gas leak or a dead animal in your vent. You may have a mold problem if you can smell mustiness.

A musty smell indicates that your air conditioning system may contain harmful impurities. Your system is a perfect environment for bacterial development since it is dark, damp, and full of moisture.

These signs indicate that your air conditioner is dispersing harmful mold spores into each area of your house. These spores can seriously harm your health, especially if someone in your household has allergies.

How Can I Avoid Smells in the Future?

Routine maintenance is the best way to solve issues before they become irreparable or dangerous. It’s the same concept with smells. A technician can catch a dangerous issue like a gas leak before it has cause for concern.

The HVAC contractors at Cardinal Heating and Cooling care about your air quality and home comfort! Schedule service with us to experience 100% satisfaction guaranteed!


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