musty smell from ac

What Causes a Moldy Odor When the Air Conditioning Activates?

Have you ever turned your air conditioner on and smelled a moldy or musty odor? As unpleasant as the smell may be, this is a common issue for homeowners in our area. Even so, you likely want to know what causes a musty smell from AC units and how to fix it when it happens. Keep reading to find out.

Why Does My AC Smell Musty?

Knowing the root cause when your air conditioner smells musty will let you fix the problem now and prevent it from happening again. Here’s a list of the most common causes of musty and moldy odors:


  • Mold and mildew growth due to moisture trapped in the AC system.
  • Clogged or dirty filters.
  • Stagnant water in the AC’s drain pan from improper drainage.
  • Dirty evaporator coils.
  • Blocked or dirty air ducts.
  • Leaking refrigerant, especially if the musty odor has a chemical-like scent.

How Your HVAC Ductwork Affects Your Air

The HVAC ductwork plays a significant role in the performance of your entire HVAC system. However, it can also be behind the unpleasant odor that takes over your home when your AC comes on. The ductwork in your walls and attic helps deliver cool air to each room while removing the stale air from your house.

If your HVAC ductwork isn’t properly insulated and maintained, the ducts can become damaged or clogged with debris. This buildup can lead to inefficient airflow, which can cause a musty smell to take over.

If your HVAC ductwork is over 10 years old, you likely need to replace some or all of it to prevent a buildup of moldy odors or other more concerning issues. Having a technician come out to inspect your ductwork can give you peace of mind regarding the status of your ductwork and a plan for any repairs or replacements.

How to Fix and Prevent Musty Odors

If your AC smells musty, it’s time to get a professional HVAC technician out to investigate the issue. A full inspection will be able to determine which issue is causing the unpleasant odor to take over your house. Once the problem is identified, the technician can offer repair options and get your home back to smelling good.

To prevent moldy odors from an AC unit, it’s essential to perform regular maintenance on all aspects of your unit. Clean or replace the filters as recommended, check the drain pan for blockages, and have your HVAC technician perform a checkup on your unit at least once a season. They can handle cleaning the coils, drainage pipes, or other maintenance elements you may not feel confident enough doing.

Let Elite Help

Nothing ruins a day like a foul odor you can’t escape. If your air conditioner is letting off a moldy, musty smell, call Elite Heating and AC Repair immediately. One of our technicians will be out to inspect and diagnose the cause of the odor and get your home back to smelling fresh in no time.


We Provide Expert Air Conditioning Services in Las Vegas, NV

  • MM slash DD slash YYYY
  • This field is for validation purposes and should be left unchanged.