What to Do If Your AC Smells Moldy After Storm Flooding in St. Louis

If your air conditioner smells moldy after storm flooding, immediately turn it off to prevent spreading spores, then clean or replace filters, dry internal parts, disinfect with a safe solution, and schedule a professional inspection to ensure all mold and moisture are removed.

 

Why Your AC Smells Moldy After Flooding

 

When floodwater enters your home, it carries dirt and moisture into the HVAC system. Wet, dark spaces inside ducts and coils become a breeding ground for mold and mildew. Mold releases tiny particles called spores, which float in the air and cause musty smells. Breathing these spores can irritate your nose and lungs, especially for people with allergies or asthma.

 

Immediate Safety Steps

 

• Turn off your AC at the thermostat and circuit breaker to stop airflow and limit spore spread.
• Open windows and use fans to ventilate the area, helping to remove stale air.
• Wear basic protective gear such as gloves and a mask when handling damp parts.

 

Check and Change the Air Filter

 

• Locate the air filter in your return vent or air handler. A dirty filter holds dust, mold, and debris.
• Remove the old filter, inspecting it for visible mold patches or black streaks.
• Replace with a new filter rated MERV 8 or higher to trap smaller particles. Follow the manufacturer’s size and type recommendations.

 

Dry and Clean Interior Parts

 

• Use a wet/dry vacuum or towels to remove standing water from the drip pan and around coils.
• Spray a mix of mild dish soap and water on the coils and fins. Wait a few minutes, then gently brush and rinse with a spray bottle.
• Ensure the condensate drain line is clear. Flush it with a cup of white vinegar to dissolve slime and mold.

 

Disinfect to Kill Mold

 

• Prepare a solution of one part bleach to ten parts water or use a commercial HVAC mold cleaner.
• Spray surfaces lightly, avoiding electrical parts. Let the solution sit for 10–15 minutes.
• Rinse with water and dry thoroughly using towels or a fan.

 

Dry the System Completely

 

• Run the AC fan only (no cooling) to circulate dry air through ducts and components.
• Use dehumidifiers in the area around the unit until humidity falls below 50%.
• Check after 24–48 hours to ensure no moisture remains.

 

Inspect Ductwork and Insulation

 

• Look inside ducts with a flashlight for black or green spots, a sign of mold growth.
• If mold appears, duct cleaning professionals should clean or replace affected sections.
• Check insulation around ducts; wet insulation should be replaced as it can harbor mold.

 

When to Call a Professional

 

• If mold covers more than 10 square feet inside your HVAC system.
• If you still smell mold after cleaning and drying. Persistent odors mean hidden mold remains.
• If you’re unsure how to safely handle bleach or need specialized equipment.

 

Preventing Future Mold Growth

 

• Schedule regular HVAC maintenance every spring and fall.
• Keep your home’s humidity between 30% and 50% using dehumidifiers or exhaust fans.
• Replace filters every 1–3 months, depending on usage.
• Ensure proper drainage around the outdoor unit and keep the area clear of debris.

 

Many homeowners in St. Louis and Nashville tackle these steps themselves, but professional help ensures thorough cleaning and lasting comfort. If you ever feel unsure, reach out to qualified HVAC technicians who can restore your system and indoor air quality.