Did you know that the levels of some pollutants may be two to five times higher indoors than outdoors? They can even occasionally be over 100 times higher!

There are many sources of indoor air pollutants, including an ill-maintained air conditioner. Aside from polluting the air inside your home, it can also make your entire house stink.

So if your AC smells bad or even terrible enough to make you gag, don’t ignore it. These foul odors can sometimes signal your air conditioner is about to fail. Besides, the source of the stench can affect your entire household’s health.

To that end, we created this guide discussing the most common AC smells you should never ignore. So, read on to discover what they are and what to do about them.

1. Smoky or Burning Smell

Sometimes, a smoky smell from an AC is only due to a clogged filter. It may also be dust that burns off as it lands on a heat-producing component of your air conditioner.

In those instances, the smoky odor should dissipate after a few minutes. It’s not a cause for concern, but it means you should at least replace your air filter or have your AC cleaned.

A faulty capacitor is a more dangerous source of a burning smell from AC units. It’s a device that stores electricity, which it then sends to an air conditioner’s motors to start them up. When it fails, it can stop the entire cooling system or make it work harder to cool the air in your space.

Since an AC capacitor stores high voltages, it can produce a smoky or burning smell when it fails. You might see smoke from your system’s outdoor unit; this is where you can find the electronic device.

Please don’t go too near a smoking outdoor AC unit; instead, turn off the entire system immediately. Otherwise, you’ll risk severe harm since capacitors are high-voltage devices. Note that 30,000 non-fatal electrical shock incidents occur in the U.S. yearly.

Once you’ve turned off your AC, contact a licensed air conditioner repair company ASAP.

2. Musty Odor

Particulate matter (PM), an air pollutant, is a mixture of tiny solids and liquid droplets. It’s one of the primary air pollutants that 137 million people in the U.S. breathe in high amounts daily. It’s harmful because it can irritate the eyes, nose, throat, and lungs; it may even get into the blood.

Molds and their spores are some of the particles that comprise PM. They can enter your air conditioner and settle on your system’s damp surfaces. That can include your AC evaporator coils and drip pan.

With air and surface moisture, plus the right temperature, molds and their spores can grow in under a day.

So, molds may be the culprit if your AC smells musty, like old cheese or clothes that didn’t dry properly. Hire a professional AC repair company to clean and tune up your system before they can do any more harm.

Molds can also grow in air ducts and their insulating material. Ducting systems can also harbor PM, so have yours cleaned every 3 to 5 years.

3. Stinks of Vinegar

If your AC smells like vinegar, molds may again be the cause. Another possible culprit is ozone, a pungent-smelling gas composed of 3 oxygen atoms. It can result from repeated sparking or electrical arcs inside your AC system.

You may have seen or smelled ozone outdoors in the form of smog. It’s harmful because it’s an aggressive gas that attacks lung tissues. For the same reason, a vinegar-like smell from your AC can be dangerous.

To be safe, call an air conditioner repair specialist if your AC emits sour odors. They may have to clean the unit, replace a faulty capacitor, or fix electrical connections.

4. Smells Like Chemicals

Chlorine, a disinfecting chemical, gives freshly cleaned swimming pools their distinct smell. Bleach contains chlorine, which is why it gives off the same odor.

But if your AC smells like bleach and you didn’t clean it, it may be due to ozone. To some people, this gas can smell like chlorine.

Leaking R22 refrigerants can also be sources of chlorine-like smells from air conditioners.

According to Armstrong Air and Electric, owning an AC using R22 is reason enough to give the system some TLC. That’s because it indicates a cooling system is old and more prone to refrigerant leaks.

Leaking refrigerant can be harmful because, in high amounts, it can be an asphyxiant.

Asphyxiants are gases that displace oxygen, especially in confined spaces. Exposure to them can cause dizziness, nausea, vomiting, and even fainting. Exposure to extremely high concentrations can cause coma and even death.

At the very least, a refrigerant leak can cause poor cooling in air conditioners. It can also result in increased indoor humidity and longer cooling cycles. That can lead to frozen evaporator coils, an AC leaking water, and higher energy bills.

5. Putrid Stench

A putrid smell is a sign of decomposition, and if they’re coming from an AC, it can signal a decaying dead animal. An example is if a rodent (i.e., mouse or rat) dies inside your air conditioner or air ducts. As it rots, it emits gases such as ammonia, cadaverine, hydrogen sulfide, and putrescine.

All those gases smell foul to humans and can be enough to make you sick to your stomach. However, they’re attractive to many insects, especially carrions. So if there’s a dead rodent in your AC system, it can invite other pests into your home.

Don’t let that happen; call an air conditioner repair company to inspect your unit. Have them remove the source of the stench and then clean and disinfect your AC and air ducts.

Never Ignore These Foul AC Smells

As you can see, foul AC smells signal many things, from electric malfunctions to mold growth. They can also be due to chemical emissions, refrigerant leaks, or even dead animals. Regardless of what causes them, most of these odors are dangerous, so never ignore them.

Instead, call a licensed air conditioning repair specialist to check your system ASAP.

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By Manali