Why Your Air Conditioner Smells Musty and 3 Best Ways to Fix It

Air Conditioning

A musty foul-smelling air conditioner is the last thing you ever want to come home to after a long hard day. But it is happening right now and right up your nose, demanding your attention.

How can a modern and expensive home device develop such odor? What could be the risk factors if you decide to ignore it? And if your air conditioner smells musty, are there ways to get rid of the smell fast? And how could you keep it from happening again once you eliminate the musty smells?

Let’s lay these questions for discussion so we can help you fight away this smelly AC problem and give you the freshest-smelling home possible! 

air conditioner smells musty

Why Your AC Smells Musty and How to Eliminate the Odor Fast

The main culprit for a musty-smelling air conditioner is the excess water in AC components that causes bacteria to grow and accumulate. When mold and mildew build up in the evaporator coil, drip pan, or drain line, they release a stale smell that spreads in your home.

To remove the musty smell:

  1. Clean the evaporator coil, drain pan, or drain pipe. These are the common places where excess water is found and where bacteria and fungi multiply.
  2. Wash or replace the AC air filters to remove dust or dirt buildup so that bacteria and fungi will have less to feed on.
  3. Seek the services of an HVAC professional thorough job of cleaning and servicing your unit.

Once you have eliminated the smelly problem, prevent the musty odor from coming back by:

  1. Keep your cleaning schedule regular even if you have not smelled any unpleasant odor from your AC.
  2. Locate the source of the excess water or moisture buildup. 
  3. Contact your trusted HVAC technician to do regular maintenance and checkup.

Understanding Your Air Conditioner

Before we go into the specifics of the smelly situation, it is best to understand how a sophisticated appliance such as an air conditioner can produce such a foul odor.

It is indeed puzzling how a mechanical appliance could be a source of a nasty smell. After all, it is just wires and mechanical parts inside the air conditioning, right? Not entirely. Let’s discuss briefly how your air conditioner works and what elements in the process could be the culprit of the musty smell.

Air conditioning systems come in many shapes and forms–central air conditioners, split-type, window air conditioners, and portable ones. However, their cooling processes do not differ that much from one another. 

The AC’s cooling process can be generally outlined by these steps:

  1. The thermostat reads the temperature of the room and finds it warmer than the comfortable setting it is programmed. For example, if you set your thermostat at the preferred temperature of 78 Fahrenheit, and it is currently 90 F in your home, the thermostat will signal the air conditioner to initiate the cooling and lower the temperature.
  2. The AC then draws the warm air from the room using the fan motor. The sucked-in air is pushed by the fan to pass over the evaporator coil for cooling.
  3. The evaporator coil houses the refrigerant, the cooling substance that absorbs the heat from the warm air and releases it to the outside air. The refrigerant can switch back and forth from a low-pressure gas to a high-pressure liquid as it interacts with heat.
  4. The previously warm air is now free from the heat, thanks to the refrigerant, and is blown back to the room with a much lower temperature.
  5. The four steps above are called the refrigeration cycle, and it happens several times during the day until the thermostat setting is reached. Once the preferred setting is met, the thermostat will signal the air conditioner to stop until the temperature rises again.

This seemingly simple process has several moving parts along the way but happens efficiently in the background to successfully regulate your home’s temperature making it pleasant.

How Moisture Plays in the Cooling Cycle

At this point, you might ask, “In what part of the cooling process could the musty smell come in?”  

We purposely left out one important bit in the refrigeration cycle as it deserves a separate discussion. The warm air drawn in by the AC at the beginning of the process has a significant amount of moisture content.

Yes. Although invisible to the eye in its gaseous state, warm air can contain more water vapor than cooler air. This moisture is in fact what makes the warm air uncomfortable to be around in as your sweat does not evaporate easily in a humid environment.

When the warm air touches the cold evaporator coils of the AC, the moisture in it condenses and changes from being a vapor to liquified water. The water is supposed to be redirected to a drain pan or drain line and typically sent outside.

But this condensation inside the air conditioner could clog or not drain properly, inviting bacteria to develop. Such bacterial growth then results in a foul, musty odor that contaminates your air.

Can bacterial growth impact the performance of your air conditioning, the smell and quality of the air you breathe, and most importantly your family’s health? Let’s walk you through the answers to these intriguing questions. 

Common Culprits of Why Your Air Conditioner Smells

The presence of water, especially excessive amounts of it, in places that are supposed to be dry is the leading culprit of the musty smell in your home. It could be a leak in your plumbing system, dampened and mucked up carpet, and finally, your HVAC’s water not properly disposed of.

How does excess water in the air conditioner translate to a musty odor?

Mold & Mildew

Mold is a fungal growth that develops and thrives in wet or decomposing organic matter. It especially loves such damp and dirty places because these got all their need for survival: water and food sources. Mold can eat just about anything: from dust to any kind of dirt left inside the air conditioning system.

Mildew is a term somewhat used interchangeably with mold but it has in fact unique characteristics that distinguish it from mold. 

For example, mildew typically presents itself in gray or white colors, but mold can appear as black, deep green, purple, brown, pink, white, gray, orange, yellow, or even red. Mildew is also commonly flat and powdery, while mold is somewhat embossed in surfaces, and looks slimy or fuzzy in texture.

But the presence of both mold and mildew in your air conditioner is an indication of bacterial growth. As mold and mildew grow and reproduce, they produce microbial volatile organic compounds or MVOC. One familiar type of MVOC called mycotoxins has a musty smell that you know so well and hate.

To recap why your air conditioner could be smelling musty these days: 

  • Your air conditioner removes excess moisture in the air. 
  • There could be clogging or misrouted condensation from your AC that gets stuck in the system.
  • The extra water plus dirty AC invites mold and mildew to grow and propagate.
  • Mold releases mycotoxin while growing spores or during reproduction. 
  • Mycotoxin produces a musty odor. 

Now that we have solved the mystery of where that nasty mildew smell is coming from, let’s now talk about its effect on your health if neglected. 

Why Musty Smells in HVAC is Damaging to Your Health

Let’s face it. There is mold in virtually any place on earth and we cannot totally avoid it. But what if we just ignore the smell and the little black growth here and there? Would it really be that bad? 

Even though people may perceive odors differently, being exposed to bad smells alone can already result in health problems. Strong odors can irritate the nose, eyes, throat, and lungs. Horrible smells can also trigger migraine or nausea in some. 

In some cases, prolonged exposure can cause mental health issues such as anxiety, mood swings, and increased stress level.

But musty smells brought on by mold and mildew have another remarkable hazard. Mold, if inhaled by a person allergic to it can prompt mild allergy symptoms. These include itchy and watery eyes, coughing, sneezing, wheezing, headache, weakness, and difficulty in breathing.

With continuous exposure to large amounts of mold spores could even lead to more severe allergic reactions such as lung infections, anaphylaxis, lung scarring or bleeding, liver failure, kidney problems, and blood complications.

Truly, we are no longer just talking about an unpleasant smell from your air conditioner, but a life-threatening situation that needs immediate action. What could be done to stop it from endangering your family’s health? 

Neutralize the Odor of Your Air Conditioning Now

We discussed earlier how a musty AC indicates bacterial growth build-up. We also touched on how bacteria and fungi like mold and mildew feed on water and all kinds of organic waste matter. So the best way to stop the smell is to eliminate the fungus and starve it from its food sources. How?

There are three ways you can go about it:

  1. Clean the evaporator coil, drain pan, or drain pipe. 

Why? These are the common places where excess water can be found making it an ideal home for bacteria and fungus to multiply.

  • Go straight to where the fungus and bacteria inhabit the air conditioning system and eradicate them by cleaning. 
  • Use a mild detergent and warm water as a cleaning solution. Some use vinegar to add potency to their cleaning agent.
  • Spray the solution on the evaporator coil and wait a while for the solution to soak up the dirt and loosen. 
  • Remove the build-up with a cloth or soft brush.
  • Continue reapplying as necessary.
  1. Wash or replace the AC air filters. 

Why? Air filters contain dust, dirt, pet dander, pollen, and other small particles that build up over time and clog the air conditioner. By removing these pollutants from your filter, bacteria, and fungi will have less to feed on. 

  • Turn off the AC and remove the filter from the unit.
  • Wipe off the visible dust and dirt buildup or vacuum it to reach narrow spots.
  • Gently wash the filter with water or with the vinegar and warm water solution mentioned earlier. Do not use a power hose to hose down the filter to avoid damage.
  • Let the filters dry before putting them back into the AC unit.
  • Replace worn-out filters or if they already have visible holes in them.
  1. Seek the services of an HVAC professional.

Why? An HVAC repair and maintenance certified expert can do a much thorough job of cleaning and servicing your unit, including the ducts and vents. They can also readily identify why your air conditioner smells and other system issues that have been hiding away.

Once you have done these steps above, you should see (and smell) a significant difference in the quality of the air your air conditioner provides. But what should you do to prevent unpleasant smells from ever coming back and maintain the good indoor air quality you deserve?

Prevent Your AC From Ever Smelling Bad

As we always say, “Prevention is better than cure.” There is a strong possibility that the musty smell may come back after some time so you have to be always ahead of the game when it comes to stopping the smell. What can you do?

  1. Keep your cleaning schedule regular. Whether you do the cleaning yourself or hired a professional to do it for you, don’t skip your routine cleaning just because there is no odor apparent yet. Remember, the smell is already an indication of bacterial growth so once your nose sensed it, it means the fungus could have been existing way before that.
  2. Locate the source of the excess water or moisture buildup. The air conditioner in its efficient state should be diverting water effectively away from the system. So if water is pooling or clogging somewhere in the unit, there could a be leak that needs repair.

Contact your trusted HVAC technician to do regular maintenance and checkup. Leaks could be present in unlikely places in the AC system. To keep your cooling device in its tip-top shape and the air pristine and odorless, employ the services of a professional to perform annual services to your air conditioner.

Leave a Comment