Where Are Those Air Conditioner Smells Coming From?

woman plugging nose due to smelly air conditioner

Your cooling unit should never produce a distinct smell. However, when your air conditioner is experiencing some issues, you may notice offensive, odd, or unpleasant odors that accompany the cool air. Have a professional check it right away. This article discusses common air conditioner smells, what causes them, and what can be done to resolve this issue.

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What Is Causing That Air Conditioner Smell?

Keep reading to learn some common smells your air conditioning system might produce.

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Air Conditioning Unit Has a Mold Smell

image of air conditioner mold

One of the most common air conditioner odors homeowners reported smelling is a musty, mold-like smell. This can usually be traced to the buildup of water in the drip lines, drain pan, and ducts. The water and the indoor temperature create an environment where fungus, mold, or mildew grow and thrive. As a result, a dingy odor can be smelled around your home.

The stale air in your home can indicate that your unit has dirty air filters. If it is hot and humid in your region, moisture can develop and accumulate in the HVAC filters. This typically happens when it has been some time since you last turned on your system. Therefore, the stale air circulates throughout your home when you turn it on again.

Solution: The drain pan should be emptied regularly. If the smell persists after completing this task, call an HVAC professional to examine the unit, ducts, and lines. Water buildup in your system can also mean there’s a leak. Therefore, it is useful to have your system checked to determine why water is improperly draining. Keep in mind that annual maintenance is crucial to ensure that your central AC unit doesn’t experience these problems in the first place.

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Related Article: Major Consequences Of Not Replacing Your Home Air Filter

Air Conditioner Emits A Burning Smell

If you notice a  burning odor permeating your house,  it is possible that you’re facing a burning air conditioner part. A defective cable, motor, or wire can be the cause. It may also be because you haven’t switched on your air conditioner for an extended period. Turning it on exposes the dust accumulation in it to high temperatures, resulting in a burning smell. If this is the case, don’t worry as the smell should disappear soon. If it doesn’t, turn the system off immediately and contact an HVAC professional.

Solution: Don’t conduct a do-it-yourself repair on your air conditioner that’s producing a burning smell. Hire an HVAC professional to help you. 

Related Article: How Do Ductless Air Conditioners Work?

Air Conditioner Produces Cigarette Smoke Odor

person smoking cigarette indoors depicting air conditioner smell

If someone smokes in your home, the air conditioner will suck in the smoke particles and the air filter will trap them. However, switching on your air conditioner can loosen these particles so they can mix with the conditioned air. They can escape through the vents, so you will notice a cigarette smoke smell around your home even if no one is smoking.

Solution: Open a window if you are going to smoke indoors to lessen the smell of cigarettes. Better yet, step outside your home if you are lighting a cigarette. Keep in mind that your air conditioner should be cleaned weekly or bi-weekly if you are a smoker. Wipe dirt and debris away from its surface. You should also ensure that your air conditioner receives an annual AC tune-up, preferably every spring. 

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Rotten Egg Smell Coming From Air Conditioner

A dead animal in your air conditioning ducts or the outdoor unit can result in a rotten egg smell around your home. The decomposition of a body causes the release of gasses with a foul, rotten smell. Birds, rodents, and other small animals may have gotten inside your air conditioner and died there. This will cause the rotten egg smell permeating in your home.

Solution: Search for the dead animal in your air conditioner and ductwork. It should be removed carefully. Your system should also be sanitized so that all traces are removed. If the dead animal is in a hard-to-reach area, call a dependable HVAC technician to help you. They have the correct tools and extensive experience to examine, clean, and sanitize your system. They will make sure that the system is pest-proof so it doesn’t occur again.

Related Article: What Does An Air Conditioner’s SEER Rating Actually Mean?

Air Conditioner Gas Smell

Methyl mercaptan depicting natural gas leak

A gas odor should never be ignored. You may be facing a gas leak, which is exceptionally dangerous. Natural gas doesn’t have a scent, so manufacturers add methyl mercaptan to it. This substance emits a rotten cabbage smell, warning homeowners of a gas leak. Remember that this chemical is an irritant, so exposure has several adverse effects. Some of these are dizziness, headaches, skin and eye irritation, nausea, and respiratory ailments. It can be fatal to be exposed to methyl mercaptan for long periods.

Solution: Switch off the gas supply as soon as you suspect a gas leak. Open the windows to ventilate your home properly. Evacuate your home after opening windows and call your gas company and a reliable HVAC technician immediately. Gas can ignite easily, so never light up anything while the gas smell still lingers inside your home.

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Related Article: Why Is Smoke Coming Out Of The Vents When AC Is On?


An air conditioner can experience problems, causing the unit to emit different smells. Several of the odors are harmless, but others shouldn’t be neglected. Some severe and likely fatal issues may cause them. Cleaning and changing the filter may remove some smells, while some require a professional HVAC technician to resolve them.

Don’t neglect any smell from your air conditioner. Having the problems resolved right away will ensure that health problems are prevented. It also helps keep you from having to spend money on costly repairs or replacements in the future.

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