Why Does the Air Conditioner Smell Bad? 3 Ways to Fix AC Smells

My Air Conditioner Smells Bad!

You arrive home after spending time outside on a hot and humid day. All you want is to relax in comfort with the air conditioner blowing cool refreshing air around you. The last thing you expect or want is a putrid smell assaulting your senses when you turn on the AC. “Why does the air conditioner smell bad?" you desperately ask yourself. Shortly followed by "What did I do to deserve a smelly air conditioner?”

There are various reasons why your air conditioner could be blowing foul-smelling air to your living space. Determining what kind of unpleasant smell your AC is producing can help you identify the cause so you can resolve it quickly.

Our sense of smell and what it perceives in the surroundings are critical to healthy living. Medical experts say that what our olfactory organs detect from the air can impact our metabolism, nutrition, moods, and even our day-to-day safety. It is essential to maintain an environment free from bad odors whether natural or chemical.

The way air conditioners are designed to circulate air should reduce the risk of spreading a bad smell from one source point to the entire house. So if your air conditioner smells, exercise caution when investigating the source of the bad odor and do not be hasty to try to solve it on your own without the proper equipment and gear. Burning smells or gaseous odors are especially hazardous to health. It is always best to seek professional help from a trusted technician in dealing with an odd-smelling air conditioning system.

An air conditioner could be your best friend and your worst enemy at the same time when it comes to indoor air quality. Its process of cooling works best in airtight spaces because it recycles the same air in your home over and over until it is cooled to the temperature on your thermostat.

Yes, you read it right: The air conditioner recycles the same air within your house. No, it does not bring fresh air from outside.

Why does the air conditioner smell bad

If you do not know it already, all AC units function the same way, regardless of what brand it is. It draws in the warm moist air from your indoor space and circulates it inside its mechanisms. With the help of the cooling gas-liquid refrigerant, the heat and excess humidity are separated from the sucked-in air. The removed heat is expelled outside, while the now chilled air is blown back inside the house.

This is good news for you because no matter what the temperature and level of humidity are outdoors, your AC will maintain your preferred temperature dictated through your thermostat. As long as the windows and doors are closed and gaps are sealed, air conditioning can also reduce your exposure to outdoor pollution and allergens that could be dangerous to some.

The bad news is when a foul smell from whatever source mixes in with the indoor air, the AC will not discriminate and will circulate the odor around the house. Unless the odor is  caused by big enough particles that the AC can filter and trap, the stink which is carried by tiny molecules can roam freely around your breathing space.

How quick and skillfully you deal with the source of the bad smell will determine how safe and healthy your family’s breathing air is going to be.

What the Odor From Air Conditioners Can Tell You

Among our five senses, our sense of smell could be the most mysterious according to science experts. Dr. Gary Beauchamp of Monell Chemical Senses Center in Philadelphia, who focuses his studies to taste and smell, was interviewed by News in Health (NIH), an online newsletter from the National Institutes of Health. He shared that there is an estimated number of 10,000 to 100 billion odors that a human can smell. 

We have a limited number of odor receptors while there are countless minuscule molecules in the air that we breathe. But the vast diversity of what we can smell is because a single minute molecule can stimulate “specialized sensory cells” within the nose which then activate a mixture of odor receptors, “creating a unique representation in the brain of a particular smell,” NIH printed.

What makes our olfactory sense more amazing is that odor could be relative, which means that two individuals can both smell the same thing but how they perceive it may vary. One person may smell it as unpleasant and detest it, while another person can tolerate it and even like the smell.

One thing is definite though and one fact that the medical world unanimously agrees upon: What we smell can impact our well-being. When it comes to HVAC equipment malfunctioning it could even save your life!

The New York State Department of Health website warns that “Exposure to odors could result in health effects ranging from none, to mild discomfort, to more serious symptoms. Some chemicals with strong odors may cause eye, nose, throat, or lung irritation. Strong odors may cause some people to feel a burning sensation that leads to coughing, wheezing, or other breathing problems.”

If the source of the stench was not eliminated, prolonged or recurring exposure to the bad smell can even affect your emotional health. “It also could affect mood, anxiety, and stress level," the health site warned.

You will be relieved to know that health symptoms from foul smell exposures typically quickly subsides when the odors stop. The key is to detect the source and to remove it.

But how will you know what is causing the stench? Your only clue is that the odor spreads rapidly as soon as you turn the AC on. To help you with your detective work, here is a rundown of the common smelly problems associated with your AC. 

AC Smells Like “Dirty Socks”

This type of bad odor is pretty literal and easy to identify. If the air circulating inside your house when the AC is on is similar to a sweaty gymnasium, with filthy unwashed clothes spread all around, you have the notorious “dirty sock syndrome.” Coined in the 1970s, this term has become very well-known in the HVAC industry which gives you the idea of how often it occurs in American households.

  • Symptoms. A musty or damp odor when you turn on the AC. This usually happens in springtime when most residents are switching their HVAC systems from heating to cooling mode.
  • Causes. The buildup of mold and bacteria on the evaporator coil of your air conditioner because of continued use is the most common reason. There could be dust build up in your AC over time due to inadequate filtration. 

ABC News published the results of the study from the University of Oregon that 12% of bacteria were able to reproduce in the dark versus the 6.8% of bacteria that survive in a well-lit area. Hence, the dark space inside the compact coils of an AC is an ideal breeding ground for bacterial growth.

  • Effects. Mold and mildew are the top-most sources of airborne allergens found indoors. Centers for Disease Control and Prevention or CDC warns that “exposure to molds can lead to symptoms such as a stuffy nose, wheezing, and red or itchy eyes, or skin.”

If left unattended for too long, mold growth can also decrease the performance of the unit over time and leads to a shorter lifespan of even an expensive AC model.

  • What to do. Treat the problem as quickly as possible. Clean AC filters regularly, at least once a month. Depending on the severity of the mold problem, a simple routine cleaning may not suffice. Seek the help of an HVAC  professional before trying harsh chemicals in dealing with mold growth in your AC.

Check the pipes around the house for water leaks or if the drainage needs upgrading. Clean or replace your filters if necessary. Cover any exposed soil in the basement. Consider installing a whole-house dehumidifier if moisture problems persist.

AC Smells Like Exhaust Fumes

Since we are not in medieval times anymore where people use gas in almost every mechanism, we are typically alarmed when modern and expensive equipment like your AC suddenly smells like exhaust fumes or gas.

  • Symptoms. Vaguely musty and smoky with semblance to exhaust fumes or a chemical-like smell when you turn on the AC
  • Causes. The air conditioner utilizes certain fluids that can smell like exhaust fumes if they are leaking and exposed to heat. A leak in the refrigerant line is deemed by the Department of Energy as one of the most common problems with existing air conditioners. 
  • Effects. Refrigerant poisoning is serious that when inhaled, “it can cut off vital oxygen to your cells and lungs,” according to Healthline. Prolonged exposure can lead to breathing problems, fluid buildup in the lungs, organ damage, or death.

There is also the risk of Microbial Volatile Organic Compounds” (MVOCs) mixing in with the air your family breathes. MVOCs can be the source of allergic reactions, asthma, and neurological complications.

  • What to do. As soon as you detect this smell, increase the ventilation in your living space by opening doors and windows. Do not attempt to do a fix-it by yourself. Instead, call your trusted HVAC professional to locate the leak and repair it. 

Burning Smells From AC

What makes the burning smell more distinct is that when you smell something is on fire, it is almost certain that something is. This type of bad odor problem should never be ignored and must be dealt with quickly.

  • Symptoms. A smoky or burnt plastic odor when you turn on the AC
  • Causes. If your AC has not been operated for a very long time, the accumulated dust can sometimes produce a burning smell when you turn on the machine. But if the smell is that of burning plastic or wiring, it could be because of a wiring issue, overheating motor, or some internal components on fire.
  • Effects. The burnt plastic fumes can irritate your lungs and may contain toxins that could harm your health. These emissions are noted by MIT School of Engineering “to cause respiratory ailments and stress human immune systems” and can also cause cancer.
  • What to do. Turn the AC off immediately from the breaker box to make sure the power is cut. If it is a burning dust smell, it is only temporary. But if the smell is caused by burning components, it is best to consult a qualified HVAC technician.

The Rotten Egg Smell

The rotten egg smell is exactly what it sounds like - blech! Although some who have knowledge of chemicals also identify it as hydrogen sulfide (H2S) gas.

  • Symptoms. A decaying smell when you turn on the AC
  • Causes. Dead rodents, critters, or birds’ nest trapped in the AC can cause this smell. A natural gas leak is another source. Mercaptan is added so residents can easily detect the leak.
  • Effects. Health effects include headache, dizziness, nausea, eye and throat irritation, fatigue, breathing problems.
  • What to do. Locate and remove the carcass if the smell is coming from a dead animal. If you suspect a gas leak in your AC equipment, open the windows to vent the odor out and call your gas company. Evacuate the area.  

The Bottom Line: Bad Smells From Air Conditioning Equipment Are More Than Just Stinky!

An air conditioner can produce a variety of unpleasant smells. These are more than just a nuisance but can let you know if there is a minor or even major issue with your air conditioning system. We wish we could say there is an easy DIY fix when your air conditioner smells bad. However, when working properly an AC should not produce or spread any odors; it more than likely is a sign of a serious problem.

Due to the electronic components, refrigerant gas, and connection to gas heating systems, if you are experiencing persistent bad smells from your air conditioner contact an HVAC contractor.

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