A white air conditioner outside a brick wall

Why Does My Air Conditioner Have a Musty Smell?

During the hot, humid summer months, air conditioning systems ensure that conditions remain comfortable indoors. When the weather is at its worst, you rely on the AC to cool things off and remove excess humidity. What you don’t expect is to notice that your house smells musty when the AC is on. However, detecting a musty smell from AC vents is a common problem. This post will help you get to the bottom of the question “why does my AC smell musty?” and tell you what you can do in the short and long term when the air cooled by your AC smells musty.

Common Causes of a Musty Smell From AC

That musty smell from your air conditioner may be caused by any of the following.

1. Broken or Aging Drain Pan

An air conditioner works by passing the warm air over condenser coils and is then cooled by a refrigerated compressor. The temperature of the air drops as it flows over the coils, and some of the moisture turns into water. The water then drips into the drain pan inside the air conditioner and is then disposed of through a hose.

Over time, normal wear and tear on the drain pan can cause it to no longer empty properly, causing the water to remain in the pan. Mold can begin to grow, and you might detect its presence as a musty smell from the AC vents. Normally, a full drain pan must be replaced by a heating and cooling professional.

Once the pan is replaced, the musty smell will usually go away.

2. Frozen Evaporator Coils

In addition to condenser coils, air conditioners contain evaporator coils that remove heat and moisture from the air before it is cooled. If dirt and debris build up in the unit, water droplets from the humid indoor air may become trapped on the evaporator coils. When the refrigerant lowers the temperature inside of the unit, the water on the evaporator coils may freeze.

A musty smell from the AC may be one of the first signs that the evaporator coils have frozen. Getting prompt service to thaw the system is key. If the problem persists, the frozen coils may cause serious damage to the unit and require expensive repairs. In addition to thawing the coils, the AC technician will likely change the filters to help prevent future freezing.

3. Excess Moisture in Ducts or Vents

When an AC system isn’t functioning optimally, moisture may accumulate in ducts or vents. This may also happen if your home suffers flood damage. Over time, the moist ductwork and vents can become a breeding ground for mold. Mold in vents can emit a musty smell and can be hazardous to your health, making it important that you call an AC technician promptly. Typically, the fix is cleaning the ducts and vents and servicing the air conditioner unit to improve performance.

4. Blockage in the Condensate Line

The condensate line leads from the drain pan to an external point like your landscaping or storm drain. If the line becomes clogged due to debris, dust or a foreign object getting stuck inside, water will build up in the line. This may allow mold to grow and give the AC a musty smell. An AC repair technician can fix the problem by removing the clog or fixing the line.

5. Your AC Unit is Too Large

When it comes to air conditioning, size matters. It’s important that the air conditioning system in your home matches the square footage. Other factors can also affect sizing requirements, such as the type of insulation you have, your local climate, the layout of your home, and how many people live there.

If your air conditioner is too large, air moves through the system at a pace that is too fast. This interferes with the AC system’s ability to dehumidify the air and means that the air in your home contains excess water. The increased moisture in the air can build up in vents, ducts, and inside of your air conditioner, encouraging the growth of mold and causing a musty smell from the AC vents.

An experienced AC installer can help determine if the air conditioner in your home is too large for your needs. If so, they can install a new system that will work more efficiently and reduce the musty smell in your home.

Why a Car AC Smells Musty

Problems with musty AC smells can occur in vehicles as well as homes. If you notice a musty smell when the air conditioning is running in your vehicle, the under-hood air intake vent may be clogged with dirt, debris and dust. When this occurs, moisture accumulates inside the air conditioning evaporator and evaporator case, leading to mold growth and a musty smell.

If your car AC smells musty, take it to an auto repair shop that specializes in your make of vehicle. Technicians can flush the evaporator case with commercial-grade bacteriostats to remove mold and bacteria and eliminate clogs.

Takeaways and Temporary Fixes

Whether it’s the AC in your home or a vehicle that smells musty, the best solution is to seek help from professional repair technicians. Professional service can get to the root cause of the musty smell and address it. In most cases, the musty smell from an AC will fade over time once the necessary service is complete.

While you’re waiting for an appointment or after a service call, you can freshen your home with Fresh Wave Odor-Eliminating products. Fresh Wave Odor Eliminating Gel is a convenient solution for musty smells from AC. Using plant-powered ingredients, the gel absorbs and neutralizes odor-causing mold molecules, freshening the air without any harmful ingredients. Check out the Fresh Wave Odor Eliminating Gel selection now and get on your way to improving the smell of your home or car.