8 Common Air Conditioner Smells — and What They Mean

YUCK, what’s that smell? A mysterious foul odor that sticks around too long can quickly become a source of embarrassment, discomfort, and confusion as you try to locate exactly where that nasty scent is coming from so you can remove it from your home. But after a while, it can seem like you’ve checked everywhere — from under the cabinets to behind the fridge and beyond — all to no avail. It’s enough to drive you crazy!

Still looking for the cause of that offensive odor in your home? We have some surprising news for you. The smell in question might be emanating from an unexpected source: your air conditioning system. If you notice this smell gets stronger when you turn up the AC or just suspect there might be something funky lurking in your air conditioner, take some time to identify possible problems using this simple guide to common HVAC smells.

Dirty Socks

Nobody likes the smell of dirty socks, except for maybe a few dogs out there. If your AC smells like foul footwear, it needs to be cleaned and deodorized. Because your condenser coils are outdoors, bacteria builds up inside condensers over time, leading to that unpleasant scent. You can open the windows and scrub down your outdoor unit carefully using a rag and mild dish soap to help reduce the odors, but calling an HVAC professional is the only way to banish the smell once and for all.

If you plan on cleaning off your unit yourself, don’t go overboard trying to “sanitize.” We know you want that disgusting smell gone for good, but never use cleaners that contain chlorine or bleach or rely on caustic ammonia or acid/alkaline solvents. These are sure to ruin outdoor air conditioners, so stick with mild dish soap or hand soap for best results.

Mold and Mildew

If you’ve ever left a wet towel in your gym bag too long or scrubbed out an old refrigerator, you’re likely familiar with the unpleasant scent of mold or mildew. Excess moisture in your air conditioning system invites mold and mildew to grow in these dark, wet places. While a slightly musty smell might seem more annoying than dangerous, mold and mildew threaten your indoor air quality since breathing in mold spores can cause health problems. An HVAC expert will inspect your system to determine the source of the leak, then clean out any unwelcome mold and mildew growth before making repairs.

Exhaust Fumes

Does it suddenly seem like you can smell those car commercials through your TV screen? At the beginning of the spring, you may smell exhaust fumes when you first switch your AC unit on after several months’ dormancy. This “burning smell” is to be expected in small quantities since it’s the smell of dust and debris burning off in the unit’s filter. However, if the smell sticks around or begins after you’ve had the unit running for a while, chemicals in your air conditioner might be leaking onto your evaporator coils, motor, or another part of your system. It’s worth it to invest in the health of your system and have an HVAC technician check out what’s going on ASAP. 


Your AC unit relies on several different chemicals to operate, including refrigerant. A “chemical-y” smell can indicate you have a refrigerant leak on your hands. Your HVAC system needs all hoses and refrigerant lines intact to operate at full efficiency, so don’t delay scheduling repairs if you start smelling unusual chemical odors in your home.

Gunpowder/“Electrical” Smell

The smell of gunpowder can be alarming to wake up to, especially first thing in the morning. If you notice this scent around your home, your AC unit may have an electrical problem, such as a blown fuse or a failing circuit board. Switch off power to the unit (if it’s safe to do so) and contact HVAC professionals before you turn it back on again.

Cigarette Smoke

Are you a smoker? If you or someone in your home smokes, your AC unit’s air filters may be prematurely clogged. It’s best to replace your unit’s filters at least once every two months during summer. If you smoke, you will need to replace them more often so that your AC system doesn’t end up smelling like a carton of cigarettes.

Death and Decay

Does your AC smell like something crawled into your unit and died? It’s gross to think about, but that might be exactly what’s going on. Some small animals seek shelter from the cold in inactive AC units during the winter, and occasionally this can result in a dead animal getting stuck in your system. The smell of decay might also be coming from trash or food residue that has become stuck in your system, most likely also because of animal activity. No matter the cause, you’ll want this problem dealt with right away, so you don’t have to hold your nose any longer!

Rotten Eggs or Gas

The smell of rotten eggs or gas is an indication you may be dealing with a natural gas leak, especially if your system is powered by gas. A gas leak is a problem that should be taken very seriously since inhaling toxic fumes can cause health problems or even death. If you notice this smell, call the fire department and evacuate all people and animals from your home. Do not return until you have been cleared to do so. Before you turn your air conditioning back on again, contact an HVAC professional for system repair or replacement. It’s better to be sweaty for a few hours rather than risk dangerous carbon monoxide gas inhalation.

Having HVAC problems such as a smelly AC unit or failing heater? Our team is here to help with any job, from large to small. For more information about our air conditioning repair services in Beckley, WV, get in touch with us today!