AC Smelling Musty? Here Are 4 Fixes to Try Before Calling in an HVAC Pro
As warmer months approach, you’re probably getting ready to turn that air conditioner back on. It’s been a while, so unless you’ve been keeping up regular maintenance, don’t be surprised if your air conditioner smells musty once you flip the switch. Beware, though — this is not how it should normally smell. Here’s what to do if you catch a whiff.
How to Fix the Musty Smell in Your Air Conditioner
Start with these three easy fixes to fix the musty smell: Replace or wash the filter, flush the condensate drain line, and empty and clean the drain pan. If the smell persists after a day, you’ll need to clean the evaporator coil with a coil cleaner. If you’re still dealing with a musty smell, seek help from a professional.
Why Does My Air Conditioner Smell Musty?
The source of your air conditioner’s mustiness can be determined based on when and where the smell happens, says Danny Pen, president of Massachusetts-based New Era Plumbing & HVAC. If the musty smell is near the AC unit and it smells all the time whether it’s running or not, the condensate drain line is most likely clogged. If the smell is coming from the vents and permeates the entire room (or multiple rooms), you’ve likely got mold on the air filter or in your home’s ducts. If the smell is the strongest when your AC is running, you might have mold on the unit’s evaporator coil.
“A clogged condensate drain line is the number-one cause of a musty AC smell, probably around 40% of cases,” Pen says. “Water sits in the drain pan, mold starts growing, and the smell spreads fast.”
How to Fix the Musty Smell in Your Air Conditioner
If your air conditioner smells musty, Pen suggests trying these three fixes first to see if that helps the smell. You can use a 1:1 ratio of distilled white vinegar and water for all three tasks below.
- Replace or wash the filter.
- Flush the condensate drain line.
- Empty and clean the drain pan.
Once you’ve done all three tasks, turn on the AC and see if the smell fades after a few hours. The musty smell could linger for about six hours, Pen says. If it’s still smelling musty after a full day, it’s time to clean the evaporator coil. This is a simple two-step process.
- Use a coil cleaner. Spray the coils with a coil cleaner to kill mold potentially hiding inside the coils, and let it sit for 15 minutes.
- Run the AC. The condensation inside naturally rinses the coils after about eight hours, so be prepared to leave it running all day.
Still getting that musty smell? It’s probably mold in the ducts, and for that, you need to call in HVAC professionals.
How to Prevent the Musty Smell from Returning
Focus on maintenance if you don’t want your air conditioner to become musty again. Pen notes that you want to aim for indoor humidity below 60%, and you should be sure that filters and drains aren’t clogged and that your drain pan is clean and doesn’t have standing water in it. Otherwise, you risk having condensation inside your air conditioning unit and a lack of proper ventilation — all of which can cause mold to grow.
“Keep humidity in check, flush the drain line with vinegar once every three months, and replace the air filters on time, before they get clogged,” Pen says. “Musty smells will return if you neglect even one of these.”
Is a Musty Air Conditioner Dangerous?
While a musty-smelling air conditioner isn’t necessarily an emergency, it can be a bit more dangerous than you might think. The mustiness is likely caused by mold, and you do not want that in your home.
“Mold that causes that musty smell is easy to inhale, and that’s bad for health,” Pen says. “The fact that it’s in the air conditioning unit that cools the air and distributes it throughout the whole room or even house makes it even worse, as it spreads mold spores everywhere, increasing exposure.”
People with allergies and respiratory issues are the most likely to be affected, especially over the long term.