Even the best air conditioners will have issues at some point or another. If you find that you’re frequently complaining, “The air conditioner stinks when I turn it on!” keep reading. We’re here to go over the different types of unpleasant smells you might be dealing with and what could be causing them.


  • Air conditioning systems will often have problems that you will have to troubleshoot during their lifetime.
  • Several causes can make your air conditioner smell bad when you turn it on.
  • Regularly cleaning your filter and air ducts will help keep your air conditioning unit from producing a foul smell.

Common Smells Coming from Your Air Conditioning System

If you have an air conditioning unit, you know that problems often pop up. Whether it’s that your air conditioner is making a loud noise when it shuts off or your air conditioner is not cooling the house, you’ll have to troubleshoot at some point in the future.

Insider Tip

You can do simple things like clean your AC vent without having to pay for an expensive technician.

Several issues can cause an unpleasant odor in your AC unit. Remember to take care of your AC to avoid these problems.

Learning how to clean a portable air conditioner is especially useful. If you’re still on the market for one, try looking into our Whynter portable air conditioner review.

Mildew Smell

This could signal mildew growth inside your unit due to excess moisture. Never ignore an air conditioner that smells of mildew because a mold issue can quickly spiral out of control. However, it could also signify that you have a dirty filter. Always check your air filter to see if it’s the reason for foul odors.


Pay close attention to any musty odor because this can signal dangerous mold spores.

Dirty Socks Smell

If you smell dirty socks, that’s a sign of stagnant water, otherwise known as dirty sock syndrome. The accumulation of water droplets can cause problems if your unit isn’t draining correctly. Have a technician come out and check out the condensate drain if you’re uncomfortable doing it yourself.

Gunpowder Smell

You might be dealing with a burnt-out blower fan. If the blower motor is gone, you’ll be able to smell the electrical issues that it causes. The blower motor forces air through the unit. Because of this, it might be the reason why your central AC is not blowing cold air, as well. As for mechanical issues, you might someday ask yourself, “Why is my ac compressor not working?”

STAT: Air conditioners (A/Cs) shipments in the United States reached a peak in 2021. (source)


Why are bad smells from an AC unit an issue?

There are a few different reasons why odd smells are cause for concern. First off, they can be a sign of a problem, such as a mold issue. They are also just plain inconvenient.

What are the signs of a gas leak?

If there’s a rotten egg smell coming from your AC, you might have a natural gas leak in your home that is coming through your vents. This can be extremely dangerous, so call your gas company immediately. If, however, it smells sweet, that’s a Freon leak, which is equally dangerous and requires an emergency visit from an HVAC professional.

What are evaporator coils?

The evaporator coils absorb heat from the air and allow you to enjoy cool air throughout your home. It is an essential part of the air conditioning unit.

How do I fix the moldy smell in my AC?

First and foremost, you’ll want to clean the different parts of your AC thoroughly and change the filter. You can also call a technician in so they can more formally diagnose the problem.

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