Can Mold Grow Inside Air Conditioning Units?

Air conditioners remove humidity from the air, but they also create condensation. That water drips into a drain pan and travels down a drain line. If the pan or line gets clogged, water sits and keeps surfaces wet. Mold spores, which are always in the air, land on those wet surfaces and start growing.

The cooling coils inside the unit are another common spot. They stay cold and damp while the unit runs. Dust and dirt that collect on the coils give mold something to feed on. Over time, a thin layer of mold can form on the coils, the drain pan, and even the ductwork near the unit.

• Check the drain pan for standing water
• Look for dark spots on the coils
• Sniff for a musty or earthy odor
• Inspect the filter for mold growth
• Watch for water stains near the unit

You can clean small amounts of mold yourself if you take safety steps. Turn off the unit and unplug it before you start. Wear gloves, goggles, and a mask so you do not breathe in spores. Use a shop vacuum with a HEPA filter to remove loose mold, then wipe surfaces with a mild detergent and water.

For mold on the coils or deep inside the unit, you may need to remove the front panel and access the interior. Check the drain line for clogs and flush it with a mixture of water and vinegar. Dry everything completely before you turn the unit back on. If you are not comfortable doing this, a mold professional can handle it.

• Turn off power to the unit first
• Wear gloves, goggles, and a mask
• Vacuum loose mold with a HEPA filter
• Wipe coils and pan with detergent and water
• Flush the drain line with vinegar and water
• Dry all parts fully before restarting

Regular maintenance stops mold before it starts. Clean or replace the air filter every month or two during cooling season. Keep the drain line clear so water flows out freely. You can pour a cup of vinegar down the line every few months to prevent clogs and slow mold growth.

Make sure the unit is sized right for your space. An oversized unit cools quickly but does not run long enough to remove humidity, leaving moisture behind. If you live in a coastal area with wet winters and dry summers, you might run your AC only part of the year, so check it after long breaks.

• Replace filters on a regular schedule
• Clear the drain line with vinegar
• Keep the area around the unit dry
• Have a pro inspect the unit yearly
• Run the fan after cooling to dry the coils