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Why Does My AC Smell? Reasons & Solutions

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Nothing is worse than trying to cool off on a hot, stuffy day and being met with a strange, off-putting smell from your air conditioning unit, especially when unsure of the cause. To find the best solution and help prevent it from happening again, it’s essential to familiarize yourself with common causes of bad-smelling AC. 

At Frasier’s Plumbing, Heating, Cooling, and Electrical, we take pride in delivering exceptional AC work to our Northern Wisconsin community. Our general AC services include installation, repair, maintenance, ductless air conditioning, and air quality.

Learn more about our comprehensive AC services by calling (715) 804-0947 today!

Where Are These Smells Coming From?

There are several reasons your air conditioner might smell foul. Some of the most common smells, along with their causes, include:


Moldy, mildewy, or musty smells are the most common odors your AC unit may produce. This is typically a result of water accumulating in the drain line or drainage system. This issue must be resolved so mold and fungus are removed and cease to grow. Additionally, musty smells can be caused by dirty air filters.

Rotten Eggs

The “rotten egg” smell coming from your unit is actually sulfur, and a gas leak causes it. This smell is due to a chemical called mercaptan that’s added by manufacturers so that you are aware of the presence of sulfur and can fix the issue as soon as possible.


Smells of burning plastic are a telltale sign that there is an issue with your AC unit. Your unit consists of an array of electrical components that, if not functioning correctly, can lead to them burning. If so, turn off your unit immediately and call a professional for help.

Exhaust fumes

Sometimes when the fluids inside your AC unit heat up, they produce a smell reminiscent of car exhaust fumes. This is most likely due to a refrigerant leak. Without a properly functioning refrigerant, your unit cannot adequately cool, leading to its lack of performance. It can also cause harm to the environment should the problem not be fixed ASAP!


Your AC unit might smell like sewage because the P-traps are drying, resulting in gases backing up into your home. Another cause could be that your sewer vent pipe has ruptured. Because sewer gases can be hazardous, this issue needs to be resolved ASAP.

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Solutions & Ways To Stop the Smell

Your AC unit may be producing odors for a slew of reasons. The first rule of thumb is thoroughly cleaning your unit, including its vent, evaporator coils, air filter, air ducts, and all other components. If the smell is due to a gas issue, your gas must be turned off immediately until the issue is resolved. Opening doors and windows to let fresh air in is a great first step for removing the foul odor.

Replacing old, worn-down parts might be necessary, and you may even need a complete unit replacement. Before issues worsen, turn off your unit and have a professional out to inspect and detect the root of the problem.

Hire a Frasier’s Professional for AC Services

Since 1918, the team at Frasier’s has prioritized the AC needs of our Northern Wisconsin family. We are five generations proudly servicing our neighbors for over 100 years, so we are confident in delivering the best AC solutions possible. We always work with honor, integrity, and professionalism, and our technicians are highly trained and equipped to tackle whatever service you need.

Howdy, neighbor! Don’t wait to schedule a service with us at (715) 804-0947.

We've Got You Covered, Neighbor! Contact Frasier's Today for Help
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Why Choose Frasier's Plumbing and Heating, Inc. 5 Generations Proudly Serving Northern Wisconsin for Over 100 Years
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  • Highly-trained and experienced team
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