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Why Does My AC Smell Musty & How to Get Rid of It?

It’s not uncommon to one day start up your AC unit and notice a musty scent. Just when you so much need that fresh, comfortable environment, the wet laundry-like smell spoils everything and can’t seem to go away. 

So, “why does my AC smell musty?” you might wonder. 

Well, if you notice such a smell from your AC, it’s probably the growth of mold or mildew in the unit. And this isn’t a good sign – both for your health and the functionality of the system.

But, what causes mold and mildew to form? Are there any other causes of the musty smell? Let’s find out:  

Top Reasons Why Air from Vents Smells Musty

If you are wondering why there’s a musty smell from AC vents in your home, here are the answers, including the best solution for each problem:

  1. Moisture in the Vents

Moisture in your unit’s air vents can be a stubborn issue, especially if you live in a humid area. Generally, moisture in the vents offers an ideal place for mildew to grow and thrive.

The worst thing is that it can grow anywhere in the vents or ducts, as long as there is moisture. This can be a grave issue for your family as it can be a source of health complications such as worsening asthma symptoms or causing allergy issues.

As such, when AC vents smells musty or moldy, you should act hastily to ensure that you get rid of the problem immediately. The best step to take here is to reach out to an HVAC technician to help inspect your system. The technician will clean the vents and ductwork to eliminate the bad smell and the danger of health risks.

  1. Full Drain Pan

A drain pan helps to collect the condensation from your AC’s cooling activities, which is then drained outside via the drain line. When the drain pan is full or is not draining the condensate properly, the stagnant water will be an excellent spot for mold and bacteria to start growing.

If this is the case, you will start smelling that awful smell or even notice some water leaking from the walls. You might also see a yellow tinge at the base of your unit. 

With these signs, it would be prudent to call a professional to inspect and offer a solution. Don’t wait until you experience some respiratory issues, such as allergies or asthma attacks, before acting.

  1. Clogged AC Drain Line

If you’re still asking yourself, “why does my AC smell musty?”, the answer may be a clogged AC drain line. As stated earlier, the drain line helps to drain the condensate from the condensate pan. And if there is a problem with the drain line, such as blockage or clogging, you can be sure to have issues.

Once the water is not getting out of the unit, it means it remains stagnant somewhere – most likely the drain pan. When this happens, mildew and bacteria will eventually start growing. Consequently, you’ll start experiencing the musty smell.

The best way to solve the issue is to unclog the condensate drain line – that is, if you have the skills to do it. But if you can’t do it yourself, calling an expert is always an excellent idea. Ensure that your drain line is cleaned regularly to prevent the recurrence of the issue.

  1. Dirty or Clogged Filters

“Why does my house AC smell musty?” — you’ve probably asked this question or heard ths question several times. And clogged air filters might be to blame!

Air filters are an essential aspect of your AC unit. They are responsible for cleaning the air you breathe, ensuring that it’s free of dust, dirt, pollen, and even some disease-causing bacteria.

In this light, you should inspect the filters as often as possible to ensure that they are still up to the task of cleaning the air. If the filters get clogged with dust or other particles, they can’t filter the air properly. Also, if the trapped dust and particles on the filter get wet, as the filters also trap moisture, this can be a catalyst for disaster.

The wet-clogged filters will cause the air in your house to smell musty every time the AC unit blows air in the house. So, if you were not sure why your AC vents smell musty, this might be the cause.

The solution here is simple. Replace the filters as recommended for your unit.

  1. Frozen Evaporator Coils

Evaporator coils are responsible for cooling the warm air in your house. Typically, when the air passes over these coils, they absorb the heat from the air, cooling it down. But, when there is no free airflow, especially due to clogged air filters, water droplets from the humid air settle on the coils.

These droplets will then freeze on these coils, which might form a breeding ground for bacteria and mold. And when this happens, you can be sure to experience the musty smell.

Regularly replacing the air filters might be the ultimate solution for this. However, you can contact a professional to ensure there is no other underlying issue, like inadequate refrigerant levels.

  1. Large-Sized AC Unit

Finally, if you’re asking, “why does my AC smell musty?”, the last potential cause is the size of the unit. Having the correctly sized AC unit for your house or space is crucial.  If you install a system that’s too large for the space, you’ll, in most cases, end up dealing with mildew and mold growth. So, while you might have done everything else right, including timely maintenance, the musty smell from AC vents will still occur.

When the system is too large, it means that it will pull in the air quite rapidly. As a result, dehumidifying the fresh air will not be sufficient. And as this happens, it gives room for the growth of mold and bacteria in vents and the ductwork, as the air traveling through the unit is always moist.

But not to worry, if this has happened to you, you can always replace your unit with the right-sized one. It might be an expensive affair, but it will eliminate the musty smell and any other issues that might accompany the mold and mildew growth. 

Let a professional assist you in identifying the right AC size for your home.

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