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The Mysterious Smell Coming from Your Air Conditioning:
What Could It Be?

If you’ve ever noticed a strange smell coming from your air conditioning, you may be wondering what it is. There are a few different things that could be causing the smell, and it’s important to identify the source so you can take care of it. Here are a few of the most common causes of unpleasant smells coming from air conditioners.

Does the AC unit smell like a car's exhaust?

This could be caused by a leaking pipe or component in the AC unit. If you notice this smell, it’s important to have a professional take a look at your AC unit as soon as possible. Basically, your AC unit doesn’t run on a combustion engine, so you shouldn’t expect it to smell like one. That said, when some of the liquids within your unit leak out and burn, they can give off a similar odor. So make sure you have someone check your refrigerant line.

If there’s a leak, the refrigerant can mix with the insulation around your electrical components. When this happens, it creates a burning odor. Not only is this unpleasant, but it can also be dangerous. This is why it’s so important to have leaks fixed as soon as possible by a professional.

Warning: Don’t wait to give us a call if something smells like it’s on fire.

If you smell something burning, it’s very important to take action immediately. This could be a sign of an electrical problem, which could lead to a fire. So make sure to disconnect the power to your AC unit and call a professional right away.

Does the AC unit smell like chemicals?

Freon is a common chemical used in AC units, and it can cause a chemical smell when it’s leaking. This is another problem that should be fixed by a professional as soon as possible. Inhaling Freon can be dangerous, so it’s not something you want to ignore. Freon is being phased out, so newer AC units may use a different chemical, but the same principles apply. If you smell chemicals coming from your AC unit, it’s best to have it checked out.


  • Checking air filters
  • Checking electrical amp pulls
  • Checking evaporation and condenser coils for cleanliness
  • Checking temperature splits
  • Checking electrical connections for weak wire connections
  • Checking freon levels

Does the AC unit smell like rotten eggs?

This is usually caused by a build-up of bacteria. Air conditioners can collect a lot of bacteria over time, so it’s important to clean them on a regular basis. You can do this yourself or hire a professional to do it for you.

That said, you might have an infestation of some sort. If your unit is located outside, it’s entirely possible that you have critters that are either living or (more likely) have died in there. Make sure to conduct a full investigation of the inside of the unit.

If the problem persists and you can’t locate the source, even after cleaning everything else, you may need to replace your air filter. A clogged air filter can cause all sorts of problems, including bad smells coming from your AC unit.

Does it smell musty or moldy?

If your AC unit smells musty or moldy, it could be because of a build-up of bacteria and fungi. More specifically, an accumulation of water in the AC unit’s drainage pan can create the perfect environment for bacteria and fungi to thrive. If you notice this type of smell, be sure to clean the AC unit and drain pan as soon as possible to prevent the growth of these harmful organisms.

Maintenance & Installation - We are here to help!

You can trust Lee Collins Air Conditioning to quickly repair your air conditioner with new replacement ac parts and keep your home comfortable 24/7. Our technicians have been with us for over 25 years and have amassed over 60 years of experience in air conditioning.

Have questions? We have answers! Give us a call directly at 602-805-1348 or schedule an introductory service call by clicking the button below.