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Why Your Air Conditioner Smells Bad and How to Fix It

The nose knows. Why does my air conditioner stink? While all air has some type of scent, some smells are clear indicators of a problem with your unit or somewhere in your ductwork. Your AC unit can smell bad for a variety of reasons. We're breaking down common smells from your AC unit, what causes them, and what to do about them.

Why Does My Air Conditioner Smell like Gasoline or Skunk?

This is by far the most alarming smell, which is why it’s at the top of the list. If your air conditioner ever smells like gasoline, it indicates there is a gas leak somewhere in your system. This issue can also present itself like a skunk smell. Be well aware that if your AC starts smelling like a skunk, you’re not mistaking the smell for something else, and it likely means there is gas leaking through your ductwork.

In this situation, immediately turn off your AC’s gas supply and call in professional help.

Why Does My Air Conditioner Stink Like Mold or Mildew?

If you can connect the stinky smells to stale mold or mildew, this is a clear sign that moisture has accumulated somewhere in your drain pipe, drain lines, or even in the ductwork and has allowed some sort of mildew to grow. This is not only bad for your unit, but also bad for anyone to breathe in and must be cleaned out.

It’s possible that the moldy, mildew smells could be due to dirty filters that need to be changed out, especially if you live in climates that have high humidity levels. Moisture can accumulate in the filters and lead to mold or mildew growth. 

Mold and mildew in your ductwork can be remedied by a few DIY steps, but it more than likely requires the attention of a professional to make sure it’s all cleaned out.

Why Does My AC Smell Bad Like Car Exhaust?

There is never a good reason why your AC unit should smell like an internal combustion engine. If you’re smelling this from your air conditioner, it’s likely due to some type of leak. Air conditioners today use certain fluids to operate and when these fluids are heated improperly, it can cause smells similar to exhaust fumes.

A refrigerant leak is one of the most common reasons for this smell, so it’s important to call in a HVAC specialist right away since running your AC unit with a refrigerant leak can cause a lot of internal damage. 

Why Does My AC Smell Like Something is Burning?

If your AC unit smells like fire or burning materials, shut it off right away. Because so many elements of your HVAC system are electrical (circuit boards, compressors, fans, power wires, etc), a burning smell means that any one—if not multiple—of these are malfunctioning. Never attempt any sort of DIY fix on this type of problem; always call in help from a professional to help keep you, your family, and your home safe.

The only exception to this rule is if your air conditioner smells hot after being off for a long time. Long periods of inactivity can allow dust to settle inside your AC unit. Turning it back on and smelling burning could simply be the dust burning off. In this case, the smells should only be temporary, so if the odor continues, is very pungent, or your AC starts to misbehave, turn it off and consult help from a professional technician.

Why Does My Air Conditioner Stink Like Rotten Eggs?

This one is bad news as well. Foul, rotten smells coming from your air conditioner usually indicate that there’s a dead animal somewhere in your AC unit. Birds, rodents, insects, or other types of small critters might like to make a home inside your ductwork. Unfortunately, they can get trapped inside and be unable to get out. As time passes, the smells become more and more unpleasant—but can also potentially cause damage, so it should be removed immediately.

While you can absolutely call a HVAC technician to find and remove the animal, you can also do it yourself by locating the source of the smell, then use a screwdriver to remove the cover. Remove any carcasses using gloves, then wipe the area clean, make sure it’s dry, and replace the ductwork.

Don’t Live with Stinky Smells

Unpleasant odors coming from your AC unit are not only unpleasant but also potentially dangerous. If your air conditioner has been smelling funny, don’t wait for serious problems to happen before calling in some help. Call John C. Flood at  (703) 752-1266, or you can contact our experts online to schedule your HVAC inspection.