Strange Air Conditioner Smells

Tampa Homeowner’s Guide to AC Odors & How To Get Rid of Them

You may notice smells when your air conditioner is running. Some AC odors are normal, and no reason to worry, but others indicate an AC problem that needs urgent attention.

Below, we explain some of the most common AC odors — what causes them, what to do about them, and how to prevent them.

Air Conditioner Smells Musty or Like Mildew

An air conditioner that smells like mildew is a sign you have water accumulating somewhere in your AC system. Your drain pan or drip lines are the most likely culprits. When water accumulates, it creates an environment where mold, mildew, and fungus can grow.

The best way to prevent your air conditioner from smelling like mildew is to schedule annual AC maintenance. Your technician will check AC drain lines for clogs and leaks. We’ll also replace air filters, a breeding ground for mold and mildew if not replaced regularly.

Air Conditioner Smells Sweet

Some forms of the refrigerant Freon have a sweet odor. If you detect a sweet smell when your air conditioner is running, you may have a refrigerant leak. Refrigerant is the coolant compound that makes your AC unit cool the air that passes through. If you’ve noticed your AC not performing well in addition to smelling a sweet odor near the unit, you almost definitely have a refrigerant leak. If this is the case, you need AC repair urgently. Not only can a refrigerant leak severely damage your air conditioner, it can also result in refrigerant poisoning for you. Call a professional for repair ASAP.

AC Smells Like Natural Gas/Skunky Spray

The familiar smell of natural gas is not actually natural gas — natural gas is odorless. What you’re smelling is methyl mercaptan, a compound that smells like rotten eggs or cabbage. It’s added to natural gas by utility companies as a safety measure to ensure immediate detection of a gas leak.

If your air conditioner smells like skunk spray or rotten eggs, you may have a gas leak. Shut off your gas supply immediately. Then, call the gas utility to alert them to the problem.

AC Smells Rotten

A foul-smelling air conditioner can be caused by a dead animal in the AC system. Birds, rodents, and insects can crawl into your ductwork, get trapped, and die. The rotten smell when your air conditioner is running is the distinct smell of a decomposing critter.

To prevent animals from getting into your HVAC units and ductwork, install air vent and flue covers, seal air ducts, and add protective mesh around outdoor condensers. Trim any vegetation around outdoor units and reduce moisture around AC units — moisture attracts mice, rats, snakes, and termites.

If you smell a dead animal in your air ducts, call a technician. Removing the carcass yourself can be tricky, and you may damage your ductwork if you’re not careful.

Air Conditioner Smells Like Urine

The distinctive urine-like odor of ammonia is hard to miss. If it smells like urine when your AC is running, the culprit is likely bacteria living in your AC unit. Bacteria break down skin cells that have gotten past your air filter and emit ammonia as a byproduct.

The best things you can do are to install a properly fitting air filter in the first place and replace air filters regularly. You can get rid of the urine smell in your air conditioner by scheduling an AC maintenance and cleaning appointment. Finally, consider installing an air purifier to keep bacteria, mold, mildew, and other microbes from growing in your HVAC system.

AC Smells Like Cigarette Smoke

If you smoke at home, your AC system may eventually start to smell like cigarette smoke, too. Your air conditioner’s filter and evaporator absorb odors from cigarette smoke. When you run your air conditioning, these odors are blown back into your home through air vents.

If you’re not a smoker, but you still smell cigarette smoke when your air conditioner is running, it’s possible the home’s previous owner was a smoker. Replacing air filters is the first step you can take to eliminate the odor. A professional like All American Home Services can provide AC maintenance and further diagnose the issue.

Your Air Conditioner Smells Like Something’s Burning

If you smell burning rubber or plastic, electrical components in your air conditioner, such as circuit boards and electrical wires, might be burning. This can occur when electrical components are damaged due to loose parts or corrosion, leading to electrical shorts and overheating.

A burning smell may also be dust burning off if your AC has been inactive for a long time. This usually isn’t something to worry about, but it doesn’t hurt to call an AC technician if you’re unsure.