Why Does My AC Smell Like Mildew?

Sometimes, a fan isn't enough when you're drenched in sweat on a hot day. Turning on the air conditioner can provide quick relief, but what if your AC smells like mildew?

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When funky HVAC smells make themselves comfortable in your home, don't give up hope. Keep reading to learn why your air conditioner smells musty and how you can resolve this issue.

Why Does My Air Conditioner Have a Musty Odor?

A musty odor typically indicates you have mold or mildew in your home. Excess dust and debris can also cause foul odors, but your air may smell stale rather than musty. You can solve a musty mystery by finding the source of the odor.

Consider each part of your HVAC system. Do your AC vents smell like mildew? Or maybe the fan smells like mildew when you run the HVAC system? You may also have mold growing in or around your air conditioner. A professional HVAC contractor can help pinpoint the culprit.

Here are some common reasons your air conditioner may smell musty.

Frozen Evaporator Coils

Take a look at the U-shaped metal pieces on your indoor AC unit and check for frost or ice. Frozen evaporator coils can restrict your HVAC system's airflow. Over time, this can cause mold or mildew — and a funky odor.

Backed-Up Drain Pan

Your AC drain pan catches moisture from condensation and then releases this liquid into your plumbing system. A clog can create a buildup of bacteria-filled water, causing mold, mildew or other problems.

Damaged Ductwork

Air flows through ducts in your home before getting released through vents. If ductwork is damaged, moisture can get trapped inside.

Dirty Filters

Filters capture dirt and debris, helping purify your home. Sometimes, condensation can make filters wet. This creates a welcoming environment for mold and other icky organisms.

Mold and mildew can develop in your indoor or outdoor HVAC system, and not just in the places mentioned above. An HVAC contractor can take a look if you can't find the mold or mildew growth on your own.

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Can a Moldy AC Unit Make You Sick?

A moldy air conditioner can pump moldy air into your house, which can make you and your family sick. If your AC smells moldy, turn off your HVAC system and contact a professional. You should also contact an HVAC specialist if you notice mold on your air conditioner, even if it doesn't smell.

It's important to treat mold growth right away. Long-term mold exposure can cause respiratory problems, headaches and eye irritation. You may even develop serious neurological problems or joint pain. Take musty odors seriously and figure out where they're coming from so you can address the cause.

There are many places mold can build up in your air conditioner, including:

• HVAC condensate pan. Also called a drain pain or drip pan, this pan collects water from your air conditioner when it falls from the coils.

• Evaporator coils. Condensation forms here and can easily turn into mold if humidity levels are high or you have a defective air conditioner.

• Air filters. Damp filters can become breeding grounds for mold, so change your filters regularly.

• Insulation liner. Moisture buildup can cause mold to grow on your AC's insulation liner.

Mold can form on nearly any part of your air conditioner, and it's not always easy to find. You may have hidden mold in your vents or ductwork if you don't see any fungi on your air conditioner.

How Do I Fix an HVAC Unit That Smells Like Mildew?

When your air conditioner is making your house smell musty, contact an HVAC professional for guidance. Fixing the smell typically requires addressing the root cause. For example, if you have mildew in your ducts, you may need new ductwork or a duct cleaning. Mold caused by restricted airflow may require an HVAC upgrade or new parts. An HVAC company can also check for clogs in your HVAC system that need attention.

Don't spray air freshener or light a candle if your house smells like mildew. HVAC smells can quickly take over your home if you don't address them quickly. Contact an HVAC company and explain that your AC smells like mildew. With professional assistance, you can enjoy inhaling fresh, clean air again when you run the air conditioner.