Why Does My Air Conditioner Smell Musty?

Many people take their air conditioners for granted. As long as they work correctly, people don’t spend a lot of time thinking about them.

However, when they start to cause problems, they can significantly affect people’s quality of life in their own homes. For example, if you have an air conditioner emitting a musty smell, this can be a real cause for concern.

If your air conditioner smells musty, this is likely due to the growth of mold and/or mildew within the system. A clog in a filter or drain line can combine with moisture to produce a very conducive environment for the growth of these sorts of pathogens, which can then circulate throughout your home.

If your air conditioner smells musty or foul in some other way, the good news is that there are things that you can do to combat the problem. Read on to find out more about what causes the problem and what you can do about it.

Reasons Why an Air Conditioner Can Smell Musty

The majority of the time, if an air conditioner smells musty, it is due to mildew and mold growth within the system.

This growth is often caused by moisture. There are a few different specific problems that can cause this issue.

Clogged Filters

In some air conditioning systems, tiny particles accumulate and settle into the filters over time.

When these particles come into contact with moisture, this can lead to the growth of mildew.

If you have an AC filter that is clogged and dirty, this could be why your air conditioner is giving off a musty smell.

Clogged Drain Lines

Within your AC system, the coils generate a certain amount of condensation. There is a condensate drain line that assists in the removal of this condensation.

If the drain line is clogged, this excess condensation can linger and help along mildew growth around the coils. The end result of this is a musty-smelling air conditioner.

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How to Remove the Musty Smell from an AC System

In some cases, you might be able to clean the air conditioner on your own.

However, you should definitely do your research so that you can take the proper precautions and minimize the risk of damage to your AC system or yourself.

The following are some steps that you can take to potentially eliminate the musty smell that is emanating from your air conditioner:

  1. Carefully take out the outer casing. This way, you will be able to see the coil, fans, and compressor within the system.
  2. Move your AC unit to a better place. You want to move it somewhere where you can keep it secure as you are cleaning it.
  3. When you have to blow compressed air, do this from a distance. You want to make sure that the system’s internal components do not accumulate any damage while you are cleaning.
  4. Use a small piece of cloth or a brush to clean off any fine dust particles located in the rear and front of the AC unit.
  5. Flush out the drip tray to get rid of the dust and debris. However, you should make sure that you don’t apply excess pressure while you are doing this.
  6. Let your AC unit dry for a couple of hours after you clean it. After this, wipe it down with a clean, dry cloth.
  7. After your air conditioning unit has dried completely, reassemble it.

You should keep in mind that there are some situations in which you should not be trying to undertake this process on your own.

If you feel like you cannot handle it or could potentially damage the unit even more or even injure yourself, you should play it safe and call a professional instead.

In some cases, there will be so much mildew that you shouldn’t expect to be able to clean it properly without the help of a professional.

In other cases, the mildew’s location will make the cleaning process very tricky for someone who doesn’t have that expertise.

Additionally, your air conditioning unit might keep producing a musty smell even after you are done because of debris and moisture collected within the ductwork and in the coil.

It is challenging to clean this on your own, so you might be better served to contact a professional if you think any of these situations might apply to your AC unit.

Different Smells That Indicate Problems Within Your Air Conditioner

In addition to a simple musty smell, there are other smells that might indicate problems with your air conditioner.

Most of the time, when something doesn’t smell right in your air conditioner, this means that there is something that needs to be fixed.

Exhaust-Like Smells

If your air conditioner is creating a smell that reminds you of exhaust fumes from a car, there is likely something wrong.

Air conditioners do not have internal combustion engines, so there is no reason why this smell should be present.

However, your air conditioner does use certain fluids that can smell like exhaust fumes when they get hot.

If you are experiencing this kind of smell from your AC, this typically means that there is a refrigerant leak.

This can compromise your air conditioner’s performance and, more importantly, release potentially hazardous chemicals into the air that you and your family members are breathing.

If you are experiencing this, you should get a professional to check on your air conditioner right away. In some cases, a leak can be dangerous.

In the meantime, before you can get someone to fix it, open the windows as much as you can and make sure that your home is well-ventilated.

This will help mitigate the smell and any hazardous effects from the leaking chemicals.

Burning Smells

If your air conditioner smells like something is on fire, this is probably exactly what it means.

There are many different electrical components within your AC unit, including compressors, power wires, and circuit boards.

If you smell burning plastic or gunpowder anytime you are around your air conditioner, it probably means one or more of these components are actually burning.

In this situation, you should immediately turn off the air conditioner and consult a professional.

You should not try to fix it yourself, because it can be hazardous. It is also possible that the smell is just coming from settled dust burning off, which is much less severe, but you won’t know that this is the case unless you call in a professional.

Rotten Egg Smell

If your air conditioner smells like rotten eggs, this is usually because there are small dead animals stuck in the unit.

Sometimes, birds, insects, or rodents can settle into your ductwork, become trapped, and die.

After they die, they will start to emit foul odors that you will smell very strongly as soon as you turn on your air conditioner.

In addition, these animal carcasses can damage different parts of your AC system.

It’s always a good idea to pest-proof your unit to avoid the situation. However, if it has already happened, you can attempt to remove the carcass yourself or call in a professional.

If you do it yourself, you will need to figure out exactly where the carcass is. A professional might be required to remove it if it is in a tricky location within the system.

Gas Smell

If you smell gas coming from your AC system, this could actually be extremely serious. Most of the time, this means that there is a gas leakage somewhere within the system. Specifically, it is usually methyl mercaptan.

Natural gas does not have a smell, but gas distributors and utility companies put methyl mercaptan into the gas to give it a distinct smell, so that people will immediately be able to tell when it’s leaking.

This makes it so that you’ll be able to act quickly and prevent any serious harm that could occur.

If you smell something that reminds you of skunk spray, this likely means that there is gas leaking and infiltrating your ductwork.

The first time you smell this, you should turn off your gas supply immediately. Then, you should contact your utility company, as they will be able to come in, figure out the source, and fix your system.


Many people don’t know this, but your air conditioner’s cleanliness is quite essential for your quality of life.

If there is musty air within your air conditioner, this air will likely end up circulating throughout your home and being very unpleasant for everyone who lives in it.

Also, mold and mildew growth within your air conditioner can release spores that can circulate throughout your home.

This can cause health problems for you and your family members that would have been entirely avoidable. The best thing to do is to address this problem immediately when it comes up.