What’s That Smell Coming from my Air Conditioner?


If an air conditioner is working properly, the air will smell clean and pure. Any odors should be investigated, as they may indicate a problem with your unit, the environment or your home. Sometimes a quick inspection is all that’s needed to find out what’s wrong, although troubleshooting by an expert is often required.

External Causes of Odor

Many air-conditioning units draw air from outside a home to the inside, and because of this any smells from outdoors can be carried in. A quick inspection of the area under, over and around your air conditioner can save you the money and hassle of calling a specialist to look for problems that may be the result of external causes.

For example:

1. Exhaust or a burning oil smell can be caused by a car, motorcycle or truck idling near your air conditioning unit. 2. A smell of gasoline could indicate a leak from a motor-vehicle nearby. 3. Bins of garbage located under or near an air conditioning unit may cause occasional rotten or even decayed smells. Disgusting Things4. A dead animal can produce putrid odors. If you find yourself having to remove a dead animal, be sure to wear protective gloves. 5. Water soaked ground on a hot day can produce a wide variety of nasty smells.

In this case, you’ll need to find the source of the water – which could be a leak from your air conditioning unit – and get it repaired.

Pools of standing water can be a breeding ground for disease, insects, and algae.

6. Certain kinds of plants can produce different smells at different times of the year. Some of these odors may be pleasant, and others may be very unpleasant. 7. Before picking up the phone, look around your a/c unit and see if you can identify what’s causing the smell.

If you find that the cause of your odor is the result of something not directly related to the air conditioning unit, you’ll have to decide whether it needs to be fixed.

Obviously, a dead animal will need to be disposed of, and water soaking in the ground will have to be cleaned up. There may be other things that you can’t do much about – it’s possible that garbage bins may not be moved or your neighbors could refuse to idle their car somewhere else.

Refrigerant Leak

Most air-conditioners are powered by electricity, not natural gas, gasoline or diesel. Any kind of exhaust smell is cause for alarm since it could indicate a potential refrigerant leak from within the unit.

Once you’ve eliminated any external causes for the odor, such as an idling car, you should call an air conditioning specialist to diagnose and repair the issue. Refrigerant leaks don’t get better on their own, and if not addressed could cause expensive damage to an a/c unit.

Dead Animal

DisgustingIf the smell coming from your air vents is an odor of rotten or spoiled eggs or curdled milk, it’s possible that an animal such as a bird, mouse, or rat crawled inside your air conditioning unit and then died.

This can happen during the winter because a sick or hurt animal could find refuge inside. Once they die, their body will begin decomposing, and when you turn on the air conditioner as the weather gets warmer, the smell will be blown throughout your house.

In this case, your air conditioner will need to be thoroughly cleaned by a professional to ensure not only that the smell is taken care of, but that any possibility of disease, mold or mildew is also handled.

 Gas Leak

If you notice a strong, skunk-like smell – it could even smell like burning sulfur – then you may have a gas leak, or it’s possible (although unlikely) that have a dead skunk somewhere in the vicinity. Get out of the house (and ensure you don’t forget your family and pets) and call the gas company immediately.

A gas leak is an emergency which can cause explosions and death. This is not an air conditioning problem; rather, the a/c unit is pumping the gas smell around your home.

Sewer Line Leak or Break

If the odor coming out of your air conditioner smells like sewage or methane, then you may have a broken sewer line nearby. There are several dangers with this condition, including the possibility of raw sewage containing diseases, bacteria, and parasites.

The problem can be an actual break in a sewage pipe or a leaky septic tank, which is a tank near or under a house that contains wastewater, organic materials, excrement, and other unpleasant things. Normally these are perfectly safe, but they do need to be emptied from time to time, and they can spring leaks caused by storm damage, roots from trees, and other things.

Exposure to sewage from a pipe or septic tank can cause any number of diseases including hepatitis, E. coli, gastroenteritis, asthma and so forth. These can be contracted by touching the bacteria and putting your hands in your mouth, breathing it, or absorbing it through the skin.

Because of this, if you smell sewage coming from your air conditioning unit, you should call your plumbing professional as soon as possible.

Fungus or Mildew (Dirty Socks)

Dirty Trash If the air coming out of your air conditioner smells moldy or like mildew, then there is most likely mold, mildew or fungus growing in the unit, vents, or filters. These smells don’t go away on their own – in fact; they tend to get worse as the mildew spreads through the unit and into your home.

This problem is caused because of the wet conditions within your air conditioning unit. Mold must have water to grow, and since air-conditioners remove water through condensation, if they are not maintained properly they can become breeding grounds for these life forms.

Mold and mildew need to be addressed quickly, as they can produce health problems, especially with people with asthma, allergy or breathing conditions. Any type of mold has the potential to trigger allergic reactions, but some molds produce toxins which cause serious issues such as pneumonia. Mold that is growing within an air conditioning unit is of particular concern, as it can be blown throughout the home.

If you smell mildew or fungus, you should call your air conditioning service company as soon as possible. Your unit will need to be cleaned, filters replaced, and checked for leaks.

Shorted Out Circuit Board

If your air conditioner puts out a gun power smell, you may have a shorted-out circuit board or motor This can happen in an older system as parts age, or it could be caused by a defect in the unit.

In this case, you may also notice the unit is not cooling as well as in the past, and it may even be smoking slightly. You should call an air conditioning specialist to get your unit repaired or replaced.

Clogged AC drain

Air Conditioner ProblemStagnant water caused by a clogged or obstructed drain in an air conditioning unit can lead to a pungent, musty smell reminiscent of stinky feet. Undrained water collects in the unit, and since it’s stagnant, algae, mold, bacteria and other things will flourish and produce a wide variety of smells.

Additionally, the growths within your a/c unit can release toxins, such as mold spores, into your house where it can be breathed into the lungs and absorbed through the skin.

When you examine the a/c unit, you may notice water droplet inside. This is normal, and a condensate drain removes the water, so it doesn’t build up. If this drain is not cleaned occasionally, it can become clogged, which will raise the humidity in your house, produce “funny” smells and even cause water damage to your home.

Cleaning the drain is occasionally overlooked by technicians during regular a/c maintenance. Make sure you ask during each visit to keep this annoyance from happening.


Air Conditioning units usually produce air which is free from odors. Sometimes things in the immediate environment, such as an overfilled garbage can or an idling car, can produce odors that you can smell throughout your home. These causes can be quickly identified and handled, and the smell should disappear.

If you smell a skunk-like odor, regardless of whether it’s coming from the a/c unit or not, indicate a possible gas leak. This is an emergency and should get your family and pets out of the house as quickly as possible, and call the gas company.

Sometimes, though, a smell indicates a problem either with the a/c unit, such as a refrigerant leak. In these cases, call your air conditioning technician to get the issue resolved. Otherwise, the problem will only get worse, and your health could be affected.

Contact Air Zero online or call us at 727-392-6111 to schedule a service call today.