How to Remove Musty Smells from a Home Air Conditioner

Lead Image for How to Remove Musty Smells from a Home Air Conditioner
  • 1-2 hours
  • Beginner
  • 25-50
What You'll Need
Garden hose
Latex gloves
Bleach or vinegar
New filters
Liquid soap
Foaming coil cleaner
Three-way clean-out valve
What You'll Need
Garden hose
Latex gloves
Bleach or vinegar
New filters
Liquid soap
Foaming coil cleaner
Three-way clean-out valve

If your AC smells musty, it’s not all in your head. Musty smells from home air conditioner units are not uncommon but that doesn't mean you should have to live with them, either.

Why Does My AC Smell?

If your AC smells musty, then it's time to find and clear the source of the bad odor. Air conditioning odors usually come from mold and mildew that accumulate from condensation on the refrigerator coils, in a clogged drain pan, or leak in the system.

However, animals can also get in the unit and die, creating a really bad odor.

Removing Musty Smells and Bad Odors

Why does my AC smell? You might wonder a lot about this question, but actually, you don’t need to have this answer.

When your air conditioner smells musty, lots of things could be the root cause of the problem. But the root cause of the problem doesn't really affect how you’re going to treat the problem.

Clean the AC Unit

hand with sink attachment cleaning AC filter

Luckily, treating musty odors from the home air conditioner unit is pretty much the same procedure, no matter what's causing the bad odor. Follow these basic steps to clean the AC unit, and, in many cases, you can remove that smell no matter what may be ultimately causing the odor.

Step 1 - Prepare the Unit

Open the covers, top, or access panels of your air conditioning unit. Using a flashlight, look inside the unit for signs of what might be causing the odor.

If you have a window unit, remove the unit from the window and place it on the ground or a flat outdoor surface. Trying to clean the AC while it's in the window is dangerous for you and for it because it can fall out of place and become damaged.

Removing access panels to a window unit may take a little more work because of the number of screws used to hold it together. Draw a diagram to indicate what screws and snaps go to what panel to make reassembly easier.

Once everything is opened up, look for any dead animals (mice, rats, bats, squirrels, snakes, etc.), decaying vegetation, mold, or mildew. Animals can be responsible for any number of weird air conditioner smells.

Step 2 - Turn Off the Power

Disconnect the AC from its power supply or make sure the AC is receiving no power. You can do this by flipping the breaker if there is no other way to disconnect the air conditioner from the power.

You want to make sure to complete this step because working on an air conditioning unit with the electricity running to it is extremely dangerous. Double-check to ensure the electricity to the air conditioner is completely turned off.

Step 3 - Clean Your Air Conditioning Unit

While wearing latex gloves, remove any visible debris or dead animals you can reach. Any large debris that can be removed by hand should be taken out, as the water you flush through the unit later might not be strong enough to flush out big pieces.

When you've removed as much of any debris as you can find, use a foaming coil cleaner and air conditioner's coil. After applying it to the inside of the AC unit, allow the foam to work for about 10 to 15 minutes.

The cleaning solution should loosen any dirt, oil, or grime inside the air conditioner. Large or stuck-on pieces you can't remove by hand can be cleaned away with a scrub brush.

Step 4 - Rinse the Unit

Rinse the unit heavily until the water from it runs clear, with no soapiness. In many cases, a thorough cleaning will fix the problem if your AC smells musty, and this may be all you have to do to get rid of the bad smell.

hands cleaning AC unit with spray water

What’s Next?

Cleaning the AC unit will take care of bad AC smells that are caused by mold, mildew, and animals that got trapped inside the unit. But if a good cleaning doesn’t handle the problem, you will need to try some additional problem-solving strategies.

Flush Your Drain Line

The AC unit can be clean and still smell bad if the source of the problem is in the condensation drain line itself. If a cleaning doesn’t solve the musty smell, flush the drain line to see if this helps.

Find and remove your air conditioner's condensation drain line. Flush the line with bleach and hot water, or with undiluted distilled white vinegar, to kill any fungi, mold, or mildew that may be in the line.

In a window unit, you won't have a line, but will be able to see the built-in drain pan and drainage hole. Make sure the pan and drain hole are clean, visually inspecting the area for signs of grime and dirt.

Use an old toothbrush to scrub away visible grime and dirt, particularly around drain pans and drainage holes, when present.

Many air conditioning units are made with two drain pans, one under the coils and a secondary pan made to catch overflow condensation., if these pans are full or near-full, they could be creating that musty smell.

Locate and empty your drain pans. And if your pans are getting full, this indicates some additional AC problem that could be caused by a clogged drain line or evaporator coils that are freezing up because the air conditioner is getting too cool for too long.

For either of these problems, you will need to consult with an HVAC professional to have the problem treated properly. DIY can take you pretty far, but even this has its limits before you’re going to need someone with skills, tools, and equipment.

Replace the Filters

person replacing AC filter

Still getting bad smells? There are more components to the air conditioning unit that could be to blame.

Find and replace any filters in your unit. If your unit uses reusable filters, clean them with hot soapy water and rinse with a diluted bleach solution of one part bleach to 10 parts water.

Check the old filters for mold and mildew. Get new filters for units that have replaceable filters.

Clean the Vents

The smell might not be coming from the air conditioner or any of its components. It could be coming from the air conditioning vents in your home.

Air conditioning vents collect hair, dust, and debris over time. While the AC is still turned off, use a screwdriver to remove all the AC vents throughout the house.

Take the vents outside and spray them off thoroughly with water to remove all dust and dirt. Scrub the vent where needed, replace the hardware if necessary, and then re-attach it to the wall.

Let the vents dry completely before you turn the AC back on.

Seal the Ducts

If you’ve treated every other part of your air conditioning system, the bad smells in your AC could actually be coming from the ducts. These are the big, silver-colored tunnels that run through the basement or attic, or both, through which the hot and cold air travel to get to the vents.

Go visually inspect ductwork in the basement, attic, and anywhere else you might see it. Look for holes, cracks, and designs of disrepair and fix these areas with duct tape.

How to Check the Results of your DIY AC Maintenance

After cleaning your air conditioner, turn it back on and test the air with a few sniffs. If the odor persists, your problem may be in your ductwork.

If the air conditioner smells bad even after you take the steps to treat the problem, you will want to consult an HVAC professional to further diagnose and treat the issue. Home AC smells, if they persist, are a clear indication that there is a problem, so don't ignore this problem.

Removing Musty Smells from Home Air Conditioner Systems

Why does my air conditioner smell musty? Many people have found themselves asking this question but what you really need to know is not the cause of the smell, but how to treat it.

Musty smells coming from the air conditioner can make every part of your home smell bad. Clean the unit to manage the smell and get back to having nice air again.

Not only will it improve your air quality to know how to properly clean and maintain the air conditioner, but it will also keep your air conditioner working more efficiently and effectively. This will help keep your energy bills low, or at least prevent spikes that result from air conditioning issues.

Home AC smells can make your entire living space feel more uncomfortable and unpleasant. Knowing to remove air conditioner smells from your home will help you maintain much better overall air quality and avoid bad AC smells.

AC Smells FAQ

air conditioner connection with mold and mildew

Why Does My AC Smell?

Your AC could have a musty smell the first time you turn it on after a few months, weeks, or even days. However, if the bad smell persists, it means that something is wrong with the unit, and it should be cleaned.

When standard cleaning isn’t enough to address the issue when the AC smells musty, you’ll need to take extra steps to further treat the problem. There are a few other things you can do to get rid of bad AC smells and make your air smell a lot fresher.

Can Animals Get into the Air Conditioning Unit?

Is it possible for small animals to actually get inside your air conditioning unit? Actually, it is.

Little animals, such as mice and squirrels, and birds, have a way of getting into very small, tight spaces and getting stuck.

They can even climb into your air conditioning unit, get stuck, and ultimately begin to cause a horrible smell. When your AC smells musty, a small animal could easily be the culprit.

There is no way to fully keep small animals from getting into your air conditioning unit, so it’s a good idea to clean it out regularly, not just when you detect an odor.

Could Something Be inside My Air Conditioning Ducts?

Clogs can happen even in air conditioning ducts. Hair, dust, and sometimes even small animals can find their way into the ductwork and end up causing clogs and bad smells.

When you've tried everything else to remove a musty smell in an air conditioning unit, consider calling in a HVAC professional to have a ductwork cleaning performed. This will dislodge and remove gunk and grime that has accumulated in there.

How Do You Know If Your Air Conditioning Condensation Line Is Clogged?

The condensation line on your AC unit could get clogged and create a musty, nasty smell. But how do you know if this line is clogged?

There are several signs to look for that indicate your AC condensation line could be clogged. If the AC unit is no longer blowing cool air or if it shuts itself off, this is an indication that too much consideration is building up and triggering a failsafe shutoff.

You can also look for standing water near and under the unit, a clear indicator that the condensation line is clogged. If you see this, turn off the AC unit until that drain line can be unclogged.

How Do You Clean Mold Out of an Air Conditioner?

When the air conditioner smells bad when turned on, mold or mildew could easily be the cause of the problem. Don’t panic when you have an odor coming from air conditioning vents, just clean it.

Thoroughly cleaning out your air conditioner unit will get rid of mold, mildew, and other problems that could be causing the bad smell. Follow the steps to clean out the unit the right way, and this will get rid of any mold that’s in there, too.

Further Reading

How to Clean Air Conditioner Filters

6 AC Mistakes You're Making Right Now

14 Free Ways To Make Your AC Energy Efficient

How to Keep the Mold Smell Away

How To Keep Your Window AC From Freezing Up

How To Troubleshoot And Repair Your Window AC Unit

How To Wire An AC Disconnect