5 Reasons Why An Air Conditioner Smells Bad When Turned On

The last thing anyone wants when they come home is to find that their air conditioner is making their house smell bad. But what does it mean when the air conditioner smells? Is it dangerous? What can you do about it?

Today’s article aims to answer all of those questions and more for you today. 

Is A Smelly Air Conditioner Dangerous?

A smelly air conditioner unit can be dangerous in certain situations. Still, regardless of whether or not it is dangerous, it’s something that you should get fixed once you notice the problem. In particular, if you notice one of these smells, it can be dangerous, and you should not ignore it.

5 Reasons Your Air Conditioner Smells Bad When Turned On

1. Mildew

If your air conditioning unit is starting to smell a little moldy or like mildew, it probably means that there is some moisture building up inside the unit, allowing mold to grow there. This could be because of a water leak inside the air conditioner itself or because of water finding its way inside the machine.

Another possible cause of mildew or musty smells coming from your air conditioner is dirty filters. You should make sure to change your filters regularly to avoid this problem.

The frequency of when you need to change the filters will be different depending on your circumstances, but here’s a quick, general breakdown of how frequently you might need to change them out, based on how many pets you have and if any occupants of the house have allergies:

  • One person with no pets or allergies: every 6-12 months
  • An average home with no animals: every 90 days
  • One pet: every 60 days
  • More than one pet or occupant has allergies: every 20 to 45 days

2. Dead Animals

A rotten egg smell, like a mildew smell, can be pretty hazardous to your health and the health of the other inhabitants or guests in your home. Generally, if you smell rotten eggs or garbage in your AC, it could mean that there is a dead animal inside the unit. 

If this is the case, however, you should not attempt to remove the animal by yourself. It can carry disease or dangerous toxins that you don’t want anywhere near you. Instead, call an HVAC technician to get the animal removed and to clean up your air conditioner so that it smells nice again.

3. Standing Water

Like the mildew smell, if your air conditioning smells like feet, the most likely cause is a buildup of moisture and water inside the unit, either due to a leak or other accident. When water is left standing for too long, it becomes dirty and attracts bugs, as well as causing mold and mildew to accumulate.

Any feet-like smells that you notice from your air conditioner should be addressed as fast as you can, not only because it can save your nose but because it can keep you and other people who come to your house from getting sick from mold.

4. Fluid Leaks

Though air conditioners do not run on gasoline, there are fluids inside them that can smell very similar to car fumes when they leak. If you notice that your unit smells like gasoline or exhaust fumes, then you should get your air conditioner looked at by a professional.

There is probably some leak or other problem that a technician will need to fix to remove the exhaust smell.

5. Electrical Failure

If there is some electrical failure in your air conditioning unit, such as the fan going out or the circuit board malfunctioning, you might get a smell like something is burning or a smell like gunpowder.

3 Ways to Get Rid of the Smell from your Air Conditioner

The most efficient way to get rid of a smell in your air conditioner is to have a professional air conditioner technician come in to look at the unit and determine what’s wrong with it that’s causing the smell. In many cases, once they fix that problem, the smell will begin to fix itself.

However, before getting to that point, you can do some simple things to try to reduce the odor by yourself before calling in the technician for a more severe problem.

Make sure to turn off the air conditioner before attempting to do most of these things, however, so you don’t end up hurting yourself.

Change the Air Filters

Like we mentioned earlier, air filters in your air conditioner can get dirty pretty quickly, and depending on how many people and animals live in your house, you’ll need to change them out more or less frequently.

If you notice a terrible smell emanating from your air conditioning unit, changing out the filters should be the first thing you do to try to fix it.

Clean the Unit

Sometimes just changing the filters isn’t enough. Unless you’re already knowledgeable about how to repair air conditioners, you probably shouldn’t be trying to take apart the machine and give it in-depth cleaning and maintenance–that should be left to the professionals. However, you can do some things to help.

Cleaning the evaporator coils with some foaming coil cleaner, for example, or flushing the drain line with some bleach, could eliminate the smell.

Get Professional Help

If the problem is still there after you’ve changed the filters and cleaned the unit, then it’s time to call in an HVAC technician, who will be able to look at your machine and determine what the problem is. Ask around to find the best service for you.

Other Air Conditioner Smells You Should Be Aware Of and What They Mean

We’ve already covered the most common smells and the reasons why they occur, but there are a couple of other odors you may need to know about:

  • Cigarette smoke: If a previous homeowner was a smoker, or if you or anyone in your household smokes, then there’s a chance that smell could get into the house’s air conditioning. To prevent this from happening, try to keep an indoor smoking minimum and do it outside instead.
  • Sewage smell: It’s gross, but sometimes sewage gets backed up, and when this happens, it can sometimes end up in the air conditioning. If your air conditioning smells like sewage, you’ll need to call in a professional to clean it up and get the gunk out.


There are many different reasons why your home’s air conditioning could smell bad, from mold to dirt to sewage to smoke. Luckily, changing your air filters regularly and keeping the unit clean are great ways to help prevent odors from developing or fixing the problem if a bad smell has already developed.

If routine maintenance operations aren’t enough to stop the bad smell, you’ll need to get a professional to come in, diagnose the issue, and fix it for you. 

Hopefully, now you’re prepared to deal with any air conditioning odor problem you might run into! Staying on top of your air conditioning unit’s health also helps ensure that the inhabitants of your home stay healthy as well.