If you’ve noticed a musty odor when your air conditioner kicks on or spotted dark spots inside your unit, there’s a good chance you’re dealing with mold in window AC units. At Rocket Air Heating & Cooling in Modesto, CA, we help homeowners every summer with AC units that are contaminated by mold. This common issue isn’t just an inconvenience—it can negatively impact your indoor air quality, trigger allergy symptoms, and even shorten the lifespan of your system.
Mold loves to grow in cool, damp, and dark spaces, which makes your window AC unit the perfect environment if it’s not properly maintained. The good news is that with a little knowledge and care, you can catch mold early, clean it safely, and prevent it from coming back.
How to Identify Mold in Window AC Units
Mold inside a window AC unit often begins with a smell. That telltale musty odor that seems to come and go with the airflow is one of the first signs something’s wrong. You might also see visible patches or streaks of black, green, or gray inside the unit. These could appear on the vents, grilles, or air filter and may even coat parts like the evaporator coil or fan blades.
Health symptoms are also a big clue. If you notice increased sneezing, coughing, watery eyes, or breathing issues while the AC is running, mold could be circulating through the air. In households with children, people older than 70, or anyone with asthma, it’s especially important to inspect and clean the AC at the first sign of trouble.
What Causes Mold to Grow in Your Window AC?
Mold growth begins when moisture meets organic material like dust or dirt. In a window AC unit, condensation forms naturally as warm, humid air passes over the cold evaporator coils. If the moisture doesn’t drain properly or the unit isn’t cleaned regularly, mold spores in the air settle in and begin to grow.
Factors that can contribute to mold growth include:
Dirty air filters
Clogged drain holes
Standing water inside the unit
High indoor humidity
Poor air circulation
Older units are more susceptible, especially if they’ve been stored without being thoroughly cleaned and dried beforehand.
How to Clean Mold in Window AC Units Safely
If you suspect mold in your window AC, it’s best to act quickly. Start by turning off and unplugging the unit. If you can, remove the unit from the window and take it outside to avoid spreading mold spores indoors.
Remove and clean the air filter. Washable filters can be soaked in warm water with dish soap and a little vinegar. Disposable filters should be replaced. Next, open the AC’s outer housing to access the interior. Use a soft brush or cloth to clean visible mold from the coils, blower fan, and plastic housing. A solution of one part white vinegar to one part water works well for light mold. For heavier contamination, use an EPA-registered mold cleaner. Always wear gloves and a mask while cleaning to protect yourself from spores and fumes.
Let all components dry completely before reassembling the unit and reinstalling it. Moisture left behind can cause mold to return almost immediately.
When to Call a Professional for Mold Removal
While many homeowners can handle minor mold cleaning themselves, some situations call for a professional. If mold is growing deep within the unit, if the odor persists after cleaning, or if the system continues to aggravate allergy symptoms, it’s time to call the experts.
Rocket Air Heating & Cooling offers thorough window AC inspections and cleanings. We use specialized tools and cleaning agents to remove mold from hard-to-reach areas without damaging your unit. We’ll also check for causes like poor drainage or mechanical issues that may be contributing to the problem.
How to Prevent Mold in Window AC Units
Prevention is the best defense against mold in window AC units. Here are simple steps to keep your system clean and mold-free:
Clean or replace filters monthly during heavy-use seasons.
Run the fan-only mode for 10–15 minutes after shutting off the cooling to dry out internal moisture.
Ensure proper drainage by tilting the unit slightly outward so water drains outside.
Vacuum and wipe down visible surfaces every few weeks to remove dust and debris.
Use a dehumidifier in damp rooms to keep humidity below 50%.
Installing a mold-resistant air filter can also help catch spores before they settle inside the unit.
Best Practices for Seasonal Use and Storage
In Modesto, window ACs are often used during the hot summer months and stored during fall and winter. Before storing your unit, always clean and dry it thoroughly. Wrap it loosely in a breathable cover—not plastic—to allow airflow and prevent condensation. Store it in a dry, temperature-controlled space if possible.
Before reinstalling it next season, open the unit and inspect for signs of dust, debris, or mold. A quick clean and filter check before the first use can go a long way in preventing problems later.
Should You Replace a Moldy Window AC Unit?
If mold keeps returning despite thorough cleaning, your unit may be beyond saving. Mold that’s deeply embedded or associated with rust, corrosion, or a failing motor may indicate it’s time to upgrade. Modern AC units are more energy-efficient and include features like antimicrobial coating, better drainage, and improved filtration to resist mold.
Additionally, if your unit is more than 10 years old, it likely consumes more energy than necessary and doesn’t cool as efficiently. At Rocket Air Heating & Cooling, we can help you determine whether repair or replacement is the smarter choice for your budget and comfort.
Why Mold in AC Units Shouldn’t Be Ignored
Mold in your air conditioner isn’t just a nuisance—it can cause real health problems, especially for those with allergies or respiratory issues. Mold spores can circulate throughout your home every time the unit runs. Over time, this can lead to chronic symptoms and a decline in air quality.
If you’ve tried cleaning your unit and still smell must or experience symptoms, don’t wait. It’s better to have your system inspected and cleaned than to risk continued exposure.
Dealing with mold in your window AC? Rocket Air Heating & Cooling is here to help. Our team of trained technicians serves Modesto and surrounding areas with expert AC cleaning, maintenance, and system upgrades. Whether your unit needs a deep clean or you’re ready for an energy-efficient replacement, give us a call, we’ll restore your comfort—and your air quality—fast.
