Odors From Your AC System: What They Could Mean

San Rafael

(415) 942-6565

Santa Rosa

(707) 452-3464

When you use your AC for the first time in the cooling season, some strange smells will emanate from it. It’s perfectly normal; however, if your unit continues to give off weird odors after a few days, there might be something amiss. Before you reach out to a pro for HVAC repair near you in Sonoma County, learn about different types of AC smells.

To help you get started, we have compiled a list of AC odors and what they mean. Take a look.

Musty Odor

A musty odor coming from your AC could indicate a potential problem with your condenser coil. More often than not, this is a sign of bacterial growth, which can form on different parts of the unit, including the evaporator coil or drain or in the drain pan or drain line.

Alternatively, a musty odor could mean you have a mold or mildew problem. If moisture collects in your system, it can foster mold growth in your ductwork. Mold does not just look unsightly, but it can also cause a number of health problems.

If you notice a musty odor coming from your AC, reach out to a professional for help. The expert will check different parts for bacterial buildup. They will get rid of the buildup and come up with a plan to keep bacteria, mold, and mildew from building up in the future.

A Vinegar-like Smell

A sharp acidic smell coming from your AC could indicate varied issues. One or more of your air filters or the condensate pan may have become clogged, or your ductwork could have mold buildup. Excess condensation can also cause the problem.

Change your filters. If the problem persists, consult your HVAC technician.

A Strong and Distinctive Chemical Smell 

If you notice a strong and distinctive chemical smell coming from your AC, your system could have a refrigerant leak. This is a serious issue. A refrigerant leak can affect your unit’s performance.

Many studies have linked exposure to refrigerants to serious health concerns. Refrigerants such as R410A can be extremely harmful to the environment.

Never handle refrigerants yourself or you might inadvertently expose yourself or others around you to hazardous substances. Leave the job to a professional. AC experts are trained to safely handle refrigerants.

The sooner you reach out for help, the better. When a refrigerant leak is detected early, it is easy to fix. If you wait too long to consult a pro, the problem may snowball into a major concern, and you may have to replace your unit.

If your AC smells like paint thinner or formaldehyde, it may be leaking fluid. Before your unit runs into a problem and malfunctions, have a technician inspect it.

If you replaced your ductwork recently, you might notice a glue odor emanating from your system. This is due to the glue used for duct installation. Run your AC fan and your ceiling and portable fans. Open your door and windows and wait for the smell to fade.

Burning or Gunpowder Smell

A burning odor coming from your AC could be caused by an overheated motor or circuit board, frayed wiring, or loose electrical connections. Ignoring the problem could prove to be a costly mistake. Your AC could stop functioning, or worse, a fire could break out. Turn off your AC immediately and call your technician.

Exhaust Fumes

If you think only your car can emit exhaust gases, you are wrong. Your AC can emit them too. Exhaust fumes coming from your AC could mean that fluid in the system is leaking onto your motor or any other part of the system that heats up during operation.

These fumes are extremely dangerous. They are a serious health hazard. Long-term exposure to exhaust fumes can lead to several health issues. If you smell these fumes, have a technician perform an inspection.

Rotten Eggs Odor

If your AC smells like rotten eggs, there could be a gas leak in your home and gas may have gotten into your ductwork. Exposure to low levels of natural gas is not hazardous, but at high levels, natural gas can crowd out oxygen in your blood, leading to unconsciousness and even death.

Natural gas is also extremely flammable and explosive. If you notice this odor, switch off your AC immediately, open your windows, and get out of your house. Call the gas company. Once it is safe to enter your home, have your technician check your unit.


If you notice an overpowering, foul odor (like rotten garbage) coming from your AC, a pest such as a rodent or bird may have died inside your ductwork. Running your AC will spread the odor throughout your home. Hire someone to remove the remains of the dead animal and clean your duct system.

John Owens Services is a leading HVAC contractor. We are committed to helping our customers keep their ACs in good shape. Our experts have years of experience servicing, installing, and replacing different types of ACs. To schedule an inspection, call 707-452-3464.

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Serving Marin & Sonoma Counties

Good plumbing, heating, and air conditioning systems are vital in every North California home. John Owens Services, Inc. is proud to be the expert plumbing company you can count on

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Our philosophy is simple, we always want to maintain equipment to give it the longest life possible. Next, we want to focus on repairing when something goes wrong. Then only as the last choice, we replace equipment when needed. That’s the John Owens Way.

San Rafael
(415) 942-6565
Santa Rosa
(707) 452-3464



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San Rafael
(415) 942-6565
Santa Rosa
(707) 452-3464