Strange AC Smells that May Indicate a Problem

After a hot day outdoors, who doesn’t love coming home to a cool, refreshing blast from their AC? But What if your nose picks up something different – A stench that takes you back to high school and smelly gym lockers. Shockingly, you trace the smell to your AC unit! Is it time to burst out the air freshener? No. That smell could help you figure out what’s wrong with your AC.

Here are some common AC unit smells and what they mean:

Burning Smell

 If your AC unit has not been used in a while, it could be burning off dust. However, if the smell lingers after 30 minutes, it could be a wiring issue, electrical, or other things. Turn off the unit immediately and call a specialist to diagnose the problem. 


A clogged filter or dirty evaporator coil could have an AC unit smelling like a trash dump. If replacing the filters doesn’t clear the smell, contact a professional.

Stinky Feet

A stale, musty smell is usually caused by mold and mildew growing in the ducts. This happens when the moisture doesn’t drain properly. While mold buildup is not harmful to the unit, it is harmful to you and can cause respiratory infections.

Sweet Smell

Antifreeze is a coolant with a sweet smell found in refrigerants. A cracked coil in the AC’s refrigerant can release this toxic chemical into your home. If you smell something sweet from your AC, turn it off immediately, open the windows and contact a professional immediately to fix the leak.

Rotten Eggs

The smell of rotten eggs can mean there’s a gas leak. Gas is highly flammable, and exposure to it can lead to loss of consciousness and even death. If you smell rotten eggs, turn off the AC immediately, open the doors and windows, leave your house and contact the gas company.

Cat Pee

When AC ducts retain moisture, molds and mildew grow in them. As they grow, they release ammonia, which can smell identical to cat pee. This mold is harmful to your respiratory health; hence, getting the unit cleaned as soon as possible is critical. 


If your AC’s outdoor condenser unit gets sprayed by a skunk, the odor could make its way into your home by circulating through the AC ducts. Turn off your unit and open the windows.

A Dead Animal

Tiny critters, like birds, rats, and lizards, can make their way into your unit and can sometimes die there. As they decay, they produce foul smells that get into your home. A professional will help you get out the carcass; nevertheless, consider looking into pest-proofing your unit because these animals can damage your unit trying to escape.

Exhaust Fumes

The smell of exhaust fumes likely means there is some type of leak in your refrigerant or motor. These fumes are highly toxic and very dangerous to your health. Contact a professional as soon as possible.

While a few of these problems can be rectified by easy DIYs, always call a professional to handle your AC problems.

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