If you’ve recently turned on your air conditioner and noticed a musty, mildew smell from the AC, you’re not alone. This is a common issue that many homeowners in Modesto, CA face—especially during the warmer months when the AC is running more frequently. At Rocket Air Heating & Cooling, we know how frustrating and concerning that smell can be. Not only is it unpleasant, but it may also be a sign that your AC system needs attention.
In this blog post, we’ll break down why your AC smells like mildew, what you can do about it, and when it’s time to call in the pros.
What Causes That Mildew Smell From AC Units?
The mildew smell from your AC is typically caused by mold or mildew growth inside your system. This often happens due to excess moisture, poor drainage, or dirt buildup in certain parts of the air conditioner.
Here are the most common culprits:
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Clogged or dirty air filters: Filters that haven’t been changed in a while can trap moisture and become a breeding ground for mildew.
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Dirty evaporator coils: The evaporator coils inside your indoor AC unit can accumulate dust and moisture, creating an ideal environment for mildew.
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Clogged condensate drain line: If the line responsible for draining excess moisture gets blocked, it can cause water to pool and stagnate.
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Poor ventilation: Limited airflow can trap moisture inside your system, allowing mold and mildew to grow.
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High indoor humidity: Moist air in your home adds to the problem by increasing condensation on internal AC components.
Signs Your AC Is the Source of the Mildew Smell
Sometimes it’s hard to tell whether that musty odor is coming from your AC or another part of the house. Here are a few ways to know for sure:
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The smell gets stronger when the AC is running.
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The odor is strongest near air vents or the indoor unit.
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Your nose gets used to the smell indoors but others notice it immediately.
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You notice visible mold near vents or around the AC unit.
If any of these sound familiar, there’s a good chance your air conditioning system is the culprit.
How to Eliminate a Mildew Smell From AC Fast
Getting rid of that mildew smell from your AC system starts with cleaning and maintenance. Here are a few steps homeowners in Modesto can take:
1. Replace the Air Filter
Start with the easiest fix. A dirty or clogged filter is one of the most common reasons for mildew smells. Replace your air filter every 1–3 months depending on usage and air quality.
2. Clean the Evaporator Coil
Use a no-rinse foaming coil cleaner, available at most home improvement stores. Follow the instructions carefully and make sure the system is turned off before cleaning.
3. Clear the Condensate Drain Line
Flush the drain line with a mixture of vinegar and water. If you’re not comfortable doing this yourself, Rocket Air Heating & Cooling can help.
4. Use a Dehumidifier
Reducing indoor humidity makes it harder for mildew and mold to grow. Aim for humidity levels between 30% and 50%.
5. Run the Fan After Cooling
Letting the fan run for 15–30 minutes after the AC cycle can help dry out condensation and prevent mildew buildup.
Preventing Future Mildew Smells From Your AC
Once you’ve dealt with the mildew smell from your AC, it’s important to take steps to prevent it from returning.
Schedule Regular AC Maintenance
Routine HVAC tune-ups keep your system clean and running efficiently. At Rocket Air Heating & Cooling, our technicians inspect the entire unit, clean the coils, check the drain line, and replace the filter—preventing mildew issues before they start.
Install UV Lights in the Air Handler
UV lights are a high-tech solution that can prevent mold and bacteria from growing on your AC coils. We can install them directly in your air handler to keep things fresh year-round.
Seal Duct Leaks
Leaky ducts can pull in warm, moist air from attics or crawlspaces, increasing the risk of mildew growth. Sealing these leaks helps maintain clean air and consistent airflow.
Is Mildew Smell From AC Dangerous?
While mildew smells aren’t always harmful, they can lead to health concerns—especially for people with allergies, asthma, or respiratory conditions. Mold spores can circulate through your home, leading to:
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Headaches
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Eye or throat irritation
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Sneezing or coughing
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Worsened asthma symptoms
According to the EPA, even small amounts of mold exposure can cause health issues in sensitive individuals. That’s why it’s important to address mildew smells from your AC as soon as possible.
When to Call a Professional for Help
If you’ve tried replacing filters and cleaning your AC without success, it’s time to bring in the experts. At Rocket Air Heating & Cooling, we offer comprehensive AC inspections and deep-cleaning services to eliminate mildew smells for good.
We’re proud to serve Modesto and surrounding areas with fast, reliable service. Whether you need a routine maintenance visit or a more in-depth repair, our certified HVAC technicians have your back.
Say Goodbye to Mildew Smells With Rocket Air Heating & Cooling
No one wants their home to smell like moldy socks. If you’re dealing with a persistent mildew smell from your AC, don’t wait—take action now. Regular maintenance, clean filters, and proper drainage are all key to keeping your air fresh and your system efficient.
Rocket Air Heating & Cooling is here to help Modesto homeowners breathe easy again. Contact us today to schedule an AC inspection or cleaning. We’ll get to the root of the problem—fast.
