Nothing beats the cool and crisp air blasting from the air conditioner, especially during the hot sweltering months of summer, or if you just want a nice, cool air fanning your face after a long day of work and commute.

As the cold air fills the room, you feel a rush of relief. But the smile on your face turns into a grimace as your nostrils are filled with an unpleasant smell.

Your air conditioning unit smells bad. And you might be wondering why.

In this article, we will look at the varying reasons behind a smelly air conditioner and the solutions you can do to resolve them.

Why does my air conditioner smell bad?

how to get rid of bad smell from air conditioner

An air conditioner that is clean and works properly shouldn’t emit a foul smell. If your air conditioner smells terrible and you hear whirring or noises that seem out-of-place, then there’s something not right with the unit.

Here are the common air conditioner smells and how you should treat them:

Air conditioner smells like a car’s exhaust fumes

You might be wondering how come your air conditioner smells like exhaust fumes when it doesn’t have an engine like that of a car. Well, your AC might not be built for road adventure but it uses liquids or fluids that smell like exhaust fumes when heated.

And most likely, a refrigerant leak is the primary cause of that smell. A refrigerant is the main cooling agent of your air conditioning system. Not only that a refrigerant leak can impact the performance of your unit but it also releases harmful chemicals into the environment.

The most common type of refrigerant is Freon. Though almost odorless, you can still detect it through its faint sweet smell.

A Freon leak is potentially dangerous so it’s better to leave the hand work to HVAC professionals who will repair it in no time.

As a preventive measure, make sure that your house is well-ventilated, and might as well open your windows to let the smell out.

Air conditioner smells like rotten eggs


If your central air conditioner smells like rotten eggs, there are two possible reasons.

The first one is that there is a dead animal stuck in your HVAC system. Birds, insects, or rodents sometimes use your ductwork as a temporary shelter. Unfortunately, they get stuck in there and die.

As their dead body decays, they start to emit a foul stench that affects indoor air quality whenever you turn your air conditioner on. Not only that they make the air around you unpleasant but their carcass can also damage the components of your air conditioners.

One of the best preventive measures to avoid this scenario is to pest-proof your home. You can always call for a professional to help you eliminate the problem or you can locate the carcass and remove it yourself.

The second reason is something that homeowners should not turn a blind eye to. The smell of rotten eggs might equate to a natural gas leak, particularly, sulfur. Natural gas is completely odorless, but manufacturers are required to add mercaptan–a type of chemical that gives its distinct ‘rotten egg odor’ for easy detection of such leaks.

If your nose catches on that smell, follow these procedures:

  • Turn off or avoid operating any electrical appliance.
  • Do not use a lighter or match and put any candle or open flame if there are any.
  • Open all windows and call your gas company immediately.
  • Turn off the gas supply. If you can’t do it, your gas company will do it.
  • Leave the building or house premises immediately.
  • Do not turn the gas on. Let the gas firm do it when they deem it is safe to do so.

Musty AC Smell

Also called dirty sock syndrome and one of the most common air conditioner smell problems, a musty air conditioner smell is caused by the accumulation of water in the drain line. It could be also because of the filthy evaporator coil suffering from bacteria or mold buildup. Dirty filters also contribute to poor indoor air quality.

You do not want the smell of dirty socks to linger in the air for long, so it is better to call your heating and cooling company to immediately address the problem. It might call for a different type of repair if there is leakage in the drainage system.

Air conditioner smells like cigarette smoke


Does the smell of stale cigarette smoke waft in the air when your turn on your air conditioning? There is one culprit for this: the smoker inside your house.

When someone smokes inside your house, the stench is absorbed in the evaporator coil and filter of your AC. When you turn your AC back on, the accumulated tobacco particles are released into the air once more, filling the room with that unpleasant cigarette stench.

To counter this, you need to keep your evaporator coil clean regularly, change the air filter every 30 to 60 days, and might as well start smoking outside.

Air conditioner smells like vinegar

An air conditioner that emits a vinegar-like odor might be due to the following reasons:

  • Electric motor problem
  • Dirty or malfunctioning filter
  • Clogged condensate pan or drain line
  • Too much condensation

Simply buying air cleaners will alleviate this problem. The enzymes found in the cleaning products will remove the bad odor right. You might want to inspect your unit if the filter needs replacing.

Air conditioner smells like burning plastic

Your air conditioner is composed of wires and other electrical components. If your air conditioner has a burning odor when you turn it on, chances are, the wires inside the unit are actually burning. Turn off your HVAC system and call your technician immediately.

Has it been a long time since you turned on the unit? The accumulated dust could also be the reason why your AC smells burnt. Burning smells caused by dust are temporary and aren’t something you should worry about.

But if the bad odor persists or returns and the unit starts to malfunction, it’s best to call your HVAC technician.

Air conditioner smells like cat pee

Even though your furry companion loves exploring around your home, it is very unlikely for your cat to pee on your air conditioner. Instead of blaming your pet for the bad stench, inspect your unit for forming molds and mildews.

Mycotoxins released by mold and bacteria growth are the ones responsible for the cat pee odor emanating from your air conditioning unit. You can get rid of the mildew using appropriate cleaning products or call a specialist to do it.

Key Takeaways

The best practice is to find out the reason first why your air conditioner emits a foul odor to know the appropriate solutions to take. Investigate first and make sure to turn off the main power before inspecting your unit to avoid electrical shocks.

Make sure that you’ve thoroughly read and understood the operating manual, have the right set of tools and have proper Personal Protective Equipment (PPE) before you DIY the repair. But, for best measure, just seek the help of professionals and technicians.

And while it is tempting to spray air fresheners or purifiers to cover the smell, it will only prolong the problem at hand. Delaying the repair might even damage your unit further, eventually causing you to buy a new one.

The next time you turn on your air conditioner and you smell something funny, you know what to do. Through this article, we hope that you have found solutions to counter the unpleasant air conditioner smell circulating inside your home. After all, you deserve that crisp, cool, and of course, sweet-smelling air fanning at your face.