Updated On

May 2, 2024

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    Your new air conditioner could smell for a variety of reasons — the most common causes are mold, mildew, refrigerant leaks, and electrical shortages/issues. Smells caused by other sources, like sewer lines or gas leaks, can circulate through your AC unit and make you think it’s an HVAC issue.

    The first step to removing the odor is determining the type of smell and finding its source. Depending on where it’s coming from, you can either clean or fix it yourself or hire a professional mold remediation company or HVAC technician to fix and clean it.

    Keep reading to find out what could be causing the smell coming from your air conditioner.

    When Should A Bad Smell Produce By Your New Air Conditioner Concern You? 

    New air conditioners often have funny smells. So, how do you know when an odor coming from your AC should concern you? Here are some of the most common reasons for a strange scent when you turn on your new air conditioner. 

    Your Air Conditioner Smells Like A Dirty Sock

    If your air conditioner smells like dirty socks, it could be caused by fungus and bacteria on your evaporator coils or in your ductwork. The smell may also be accompanied by symptoms that are referred to as “air conditioner sickness.” 

    Regardless of the age of your unit, if you notice any of the symptoms below, it may be time to take action: 

    • Dizziness
    • Headaches
    • Dry Skin
    • Respiratory Illness
    • High Blood Pressure
    • Sore Throat
    • Chest Pain
    • Difficulty Breathing

    The same bacteria that causes the foul sock smell causes air conditioner sickness. So, you should call a professional HVAC repair company to assess the problem.

    Did You Know

    If you have not had a central air conditioner for a while, there is a possibility that one of the components in your system is moldy. Due to excessive humidity in a home without air conditioning, mold and mildew can grow quickly.

    A Moldy Smell Or Musty Scent

    If you have not had a central air conditioner for a while, there is a possibility that one of the components in your system is moldy. Due to excessive humidity in a home without air conditioning, mold and mildew can grow quickly.

    You may find mold or mildew in the air ducts, too. When the air ducts become filled with unhealthy mold and mildew, it can come out when you turn on your new unit.  

    So, if you think you think your unit is moldy, you need to address it promptly. Cleaning your unit may resolve the issue, but you might also need the assistance of a professional HVAC cleaning service. HVAC cleaners have special equipment that can reach deep inside your ductwork for a thorough cleaning.

    A Fishy Smell

    Wiring issues can cause a strange fishy smell. It is a mildly offensive smell so that may go unnoticed at first. 

    If you smell something like this, you should shut the unit off and call an electrician or HVAC repair contractor. If you are running a portable or window unit, they pull a lot of power, and when you leave them running continuously, the heat can melt the wiring, circuit boards, and outlets.

    Burning or melting wiring causes the smell, and if you live in an older home, your electrical system may not be able to power your new system. 

    Sometimes, air conditioning repair professionals miss wiring problems, as they are not trained electricians. So, if an air conditioner repair technician tells you there is nothing wrong with your air conditioner, it might be time to call an electrician. 

    If there are any electrical components that need to be replaced. You should also be mindful when you plug and unplug a portable air conditioner or window unit. 

    If you cause the outlet to loosen, the wires inside the wall can touch. This contact causes them to spark, which could short your device or cause a house fire. Don’t be surprised if your HVAC technician tells you that you need an electrician. 

    A Burning Smell

    If you smell a burning odor, it is also a good idea to have your air conditioner checked by a professional. However, sometimes, new systems do have a funny smell. 

    It is not uncommon for heaters to give off a burning smell when you use them for the first time each year. This is just oil and dust being burnt off on the burner. If you smell a burning smell, you might have the thermostat set to heat instead of cool. 

    There could also be an electrical problem, like an overheating fan motor. Anytime you smell something burning, you need to identify the source. If your home is on fire, go outside and call the fire department. 

    Dirty Ductwork

    Your home’s ductwork is a system of vents, an evaporator coil, a condenser coil, a condensate pan, a drain line, an air handler, and several other essential components that make up your central air conditioning system. If any of those components are dirty, it could cause the system to produce an unpleasant smell. 

    Many homeowners use the same ductwork when they purchase a new air conditioning unit. If you have dust, debris, bacteria, and fungus growing in your air ducts, your air conditioner may smell funny. 

    A dead animal that has fallen into an air duct could cause a horrible odor to come out of your vents. Luckily, there are plenty of qualified professional duct cleaning services that can help.

    Sewage Smell

    A sewer smell could be caused by a sewer line issue. Typically, a sewer-like smell is not associated with air conditioning systems. That said, sewage smells can get pulled into your HVAC system and circulate throughout your home, which may lead you to think it’s an HVAC issue.

    In most cases, it’s not, and a plumber would be the correct person to call if you notice a sewage smell after turning your air conditioner on.

    If you want to get HVAC systems warranty protection, we recommend you choose from a trusted home warranty company. 

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    What Causes ‘Dirty Sock Syndrome’ and ‘Air Conditioner Sickness’?

    If your air conditioner has not been used for a while, fungus and bacteria can develop in the indoor air handler, air filter, air ducts, and other parts of your air conditioner. The buildup of bacteria creates a musty smell, and it can even cause you to become physically sick. 

    HVAC contractors cite this as the most common reason for a foul smell coming from your air conditioner. It is also one of the most concerning because even after you have your air conditioner professionally cleaned, you may have symptoms for some time. 

    Your indoor air quality is important because you spend the majority of your time in your home. If the quality of the air in your home is bad, it can lead to allergy symptoms like runny nose, congestion, eye irritation, and other respiratory conditions. Poor indoor air quality can also make you more susceptible to bacterial and viral infections.

    When your body is constantly fighting off an infection, it is in a vulnerable state. Don’t lose sleep and let yourself constantly feel sick and run down — if your air conditioner smells bad, take it seriously and fix it. 

    For more information on ‘dirty sock syndrome,’ take a look at this video about a couple who suffered from the condition.

    What Should You Do If Your New Air Conditioner Is Producing An Odor? 

    Any odor coming from your air conditioner that is out of the ordinary is a signal that something is not right. Due to the complex nature of HVAC systems, pinpointing the exact source of the smell might not be easy. 

    You should reach out to the HVAC service company that installed your new air conditioner. They are aware of the most and least common reasons for smells produced by air conditioners. You could also choose one of our picks for the best HVAC companies in the industry.

    By having regular tune-ups on your HVAC system, you can avoid many odors before they can affect your health or air conditioning system negatively.

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    Frequently Asked Questions

    What causes a chemical smell from a new air conditioner?

    A chemical smell in a new air conditioner can be from a refrigerant leak. If it persists, turn off your AC unit and call an HVAC company to inspect the system.

    How can I get rid of the plastic smell from my new AC?

    Some air conditioning units may have a “plastic” smell from off-gassing of new plastic pieces. In this case, just wait it out. The smell usually goes away in a few days to a few weeks.

    Can I clean my ductwork myself?

    You can try to clean your ductwork yourself, but you won’t do nearly as good of a job as a licensed duct cleaning company. They have special tools and probes with cameras that can reach deep into your ductwork for a full cleaning.

    Article Update Log
    Reviewed for accuracy, cost data, industry best practices, and expert advice by Jonathon Jachura.
    Editorial Contributors
    avatar for Alexis Bennett

    Alexis Bennett


    Alexis is a freelance writer with nearly a decade of experience covering the home services industry. She’s built considerable expertise in roofing, plumbing, and HVAC, as well as general construction and real estate matters. In her free time, Alexis enjoys coaching women’s golf. She lives in the Triad area of North Carolina.

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    Jonathon Jachura


    Jonathon Jachura is a two-time homeowner with hands-on experience with HVAC, gutters, plumbing, lawn care, pest control, and other aspects of owning a home. He is passionate about home maintenance and finding the best services. His main goal is to educate others with crisp, concise descriptions that any homeowner can use. Jon uses his strong technical background to create engaging, easy-to-read, and informative guides. He does most of his home and lawn projects himself but hires professional companies for the “big things.” He knows what goes into finding the best service providers and contractors. Jon studied mechanical engineering at Purdue University in Indiana and worked in the HVAC industry for 12 years. Between his various home improvement projects, he enjoys the outdoors, a good cup of coffee, and spending time with his family.

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