How to Check AC for Mold?

Why Mold Grows in AC Systems Across Los Angeles

Southern California may be known for dry heat, but your air conditioner creates plenty of moisture on its own. Evaporator coils pull humidity from indoor air. Condensation collects in drip pans and drain lines. Ducts trap pockets of damp air, especially in older homes throughout the San Fernando Valley and Orange County.

These conditions give mold exactly what it needs to grow. In 2026, indoor air quality remains a top concern for Los Angeles homeowners. Wildfire smoke seasons, pet dander, and dust already strain your HVAC system. Adding mold spores to the mix can trigger allergy symptoms, respiratory issues, and persistent musty odors throughout your home.

Checking your AC for mold is a straightforward task you can do yourself. Catching it early prevents costly repairs and protects your family's health.

Step-by-Step Guide to Inspecting Your AC for Mold

Start by turning off your air conditioning unit completely. This keeps you safe from moving parts and gives you a clear view of each component.

Before opening anything, pay attention to warning signs. A musty smell when the system runs is the most common indicator. Recurring sneezing, coughing, or watery eyes indoors can also point to mold. Excessive moisture around the unit is another red flag.

Remove the air filter and inspect both sides. Look for visible mold spots, dark discoloration, or dampness. A moldy or musty-smelling filter needs immediate replacement.

Use a flashlight to examine the evaporator coils. These coils cool your air and collect moisture constantly. Look for fuzzy growth, dark patches, or standing water on or around the coils.

Check accessible ductwork near vents. Look for mold, unusual discoloration, or moisture inside the ducts. Pay extra attention to duct sections in attics and crawl spaces where temperatures fluctuate.

Inspect the area around your HVAC unit for water leaks, especially near the base and drain pan. Finally, check that the drip pan is draining properly and the drain line is clear. Standing water in the pan is a breeding ground for mold.

What to Do If You Find Mold in Your AC

Act quickly when you discover mold. The longer it sits, the further it spreads through your system and into your indoor air.

For mold on air filters, replace them right away. Do not attempt to clean and reuse a moldy filter. Install a fresh filter rated for mold and allergen capture. Filters with a MERV rating of 11 or higher trap mold spores effectively.

For mold on evaporator coils or air vents, clean the affected surfaces with a solution designed for HVAC systems. A mixture of white vinegar and water also works for light surface mold. Wipe down all visible growth and let components dry completely before restarting the system.

Check the drip pan and drain line after cleaning. Flush the drain line with a vinegar solution to clear any buildup. Make sure water flows freely through the line.

After cleaning, run the system and monitor for returning odors or symptoms over the next few days.

Preventing Mold From Coming Back

Prevention is simpler than repeated mold removal. Change your air filters every 30 to 60 days, especially during heavy cooling months from May through October in Los Angeles.

Keep your drip pan and drain line clean. Flush the drain line with vinegar or a commercial treatment once a month during summer. This stops algae and mold from clogging the line and causing water backup.

Maintain consistent humidity levels indoors. Your AC already dehumidifies as it cools, but homes with poor ventilation can still trap moisture. Make sure bathroom and kitchen exhaust fans work properly.

Schedule professional HVAC maintenance at least once a year. A trained technician can inspect areas you cannot easily reach, including deep inside the ductwork and the interior of the air handler. Professional duct cleaning every few years removes accumulated mold, dust, and debris that filters miss.

When to Call a Professional HVAC Technician

Some mold problems go beyond what a homeowner can safely handle. Call a professional if you see widespread mold inside the ductwork. Duct systems in many LA-area homes run through attics that reach extreme temperatures, creating conditions where mold can spread rapidly once established.

You should also call for help if mold returns after you have already cleaned the system. Recurring mold usually signals a deeper issue like a refrigerant leak, a cracked drain pan, or poor system drainage.

Black mold or any mold covering a large area requires professional remediation. Disturbing large colonies without proper equipment can release a high concentration of spores into your home.

Season Control Heating & Air Conditioning serves homeowners across Greater Los Angeles, the San Fernando Valley, Ventura County, and Orange County. Our technicians perform thorough mold inspections, coil cleaning, drain line service, and duct assessments. Call (818) 275-8487 to schedule air conditioner maintenance or a mold inspection for your HVAC system.

Frequently asked questions

How do I know if there is mold in my AC system?

The most common sign is a musty smell when your AC runs. You may also notice dark spots on air filters, visible growth on evaporator coils or vents, and increased allergy symptoms like sneezing or coughing indoors. Inspect your filters, coils, drip pan, and accessible ductwork to confirm.

Can I clean mold from my AC unit myself?

You can clean light surface mold from filters, coils, and vents using an HVAC-safe cleaner or a vinegar and water solution. Replace moldy filters entirely. For widespread mold inside ductwork or the air handler, call a professional HVAC technician to avoid spreading spores.

How often should I check my AC for mold in Los Angeles?

Check your system at least every three months. Inspect more frequently during the heavy cooling season from May through October. Homes near the coast or in areas with higher humidity should be checked monthly during summer.

What type of air filter helps prevent mold in my HVAC system?

Filters with a MERV rating of 11 or higher capture mold spores effectively. Replace your filter every 30 to 60 days during peak cooling months. A clean, high-quality filter reduces the chance of mold taking hold in your system.

Does mold in my AC affect my health?

Yes. Mold spores circulated by your HVAC system can cause sneezing, coughing, watery eyes, headaches, and respiratory irritation. People with asthma or allergies are especially sensitive. Removing mold and maintaining clean filters improves indoor air quality and reduces health risks.