There’s nothing more annoying than not being able to figure out what is causing a bad smell in your home, especially if it’s coming from your air conditioning unit. Some of the smelly air conditioning problems are reasonably minor issues, but some smells can be a sign of something potentially dangerous. In this post, I’ll be giving you some examples of air conditioner smells and what to do to fix them.

Air conditioner smells

Rotten eggs

During the winter, small animals such as squirrels and rodents often crawl into your air conditioning ducts to find some warmth. You may find that an animal or rodent had died and decomposed in your duct. When you switch on your air conditioning, it wafts the smell throughout your home. To deal with the smell of a dead animal, you will need to find the source of the decay and remove the animal, then wash and dry the area well. If you can not locate the carcass yourself, ring the air conditioning heating engineer to remove it for you safely. Lizards have also been known to get into the HVAC system, so it’s worth bearing in mind when you are looking for dead animals!

Cigarette smoke.

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Often new homeowners complain that their air conditioner smells of cigarette smoke. The smell may be caused by someone smoking close to the air conditioners system, which can then accumulate in the filter and the evaporator coil. When you turn on the air conditioner, it makes the whole house smell like cigarette smoke. To solve this problem, you can change the filter and contact a HVAC technician to give your system a tune-up and clean.



If your air conditioning system smells of sewage when you turn it on, it could mean you have a dry P Trap somewhere, which is stopping the natural seal from the sewage. To solve this problem, you could try running all the taps in the house to bring back the natural seal.If turning on the taps doesn’t solve the problem, you may have a blocked up sewage line or a ruptured sewage vent pipe, in which case you will need to call a HVAC technician to fix the problem. Sewer gasses are hazardous, so it is vital to get this problem fixed as soon as possible if you notice your AC smells of sewage.


The smell of mold is one of the most common complaints I hear when talking about air conditioner smells. It is a common complaint, as air conditioners are designed to improve the indoor air quality by pulling the excess humidity and moisture out of the air. The smell of mold in an air conditioner is often caused by water accumulation in the drip lines or by clogged drain lines. The stagnant water accumulation, which has not drained correctly, will often cause the growth of fungus, mold, or mildew inside your system’s ductwork. A moldy smell could also be caused by moisture as a result of clogged filters. You can fix the moldy smell problem by getting your lines, ducts, and filters cleaned and getting your air conditioner serviced regularly.

Car exhaust fumes

If your air conditioner smells of car exhaust fumes, it could be caused by a leak in the refrigerant line which would cause a chemical smell to leak into the air. If the fluids used by the air purifier are heated, they can sometimes smell like the exhaust fumes of a running car. Make sure you ventilate the area well by opening the windows then call out HVAC maintenance to repair the leak.


Gunpowder is another one of the air conditioner smells that is fairly common. A smell of gunpowder usually indicates a fan motor or a circuit board failure. If you smell gunpowder, turn the unit off straight away and seek help from your HVAC contractor.

Smelly socks.

As funny as it sounds, dirty sock syndrome is no laughing matter and is one of the more common air conditioner smells. No one wants to bring their friends home to a house that smells of dirty socks! The odor may be caused by water not draining correctly; this then collects and begins to smell like a dirty sock. Call a professional to check for dirty evaporator coils and dirty drain pans.


Burning or smoke

Smoke smell is one of the more serious air conditioner smells. If your air conditioner smells of burning or smoke, it’s a good indication that some of your air conditioner components are faulty, or you may have a wiring issue. A burning smell is extremely serious, as it could lead to an electrical fire. Turn off the air conditioner immediately, evacuate your building, and call the fire brigade. You should also contact your HVAC technician to come and check your machine for signs of a fault.If you smell a faint burning smell the first time you turn on your AC, it may just be the residual dust burning off from the unit after it not being used for a while.

Ammonia or urine

If your air conditioner or window air conditioner smells like urine, it is probably not caused by urine but rather mold. Certain molds give off Mycotoxins, or byproducts which smell like urine or ammonia, these can be more dangerous than some strains of the mold. It would be best if you got your system serviced and checked by a professional.


When your air conditioner smells sour, like a vinegar smell, the problem could be from an electric motor emitting a smell. It could be due to excess condensation on the coils, a clogged filter, a broken condensate pan, or mold in the ductwork.To rectify this problem call your HVAC technician to check it out.

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Paint thinner

If your air conditioner smells like paint thinner, it may be down to one of the many fluids that are essential to the functioning of your HVAC system. Your system may be malfunctioning, causing the fluids to give off a strong chemical smell. Ask your HVAC technician to check your unit for any faults.