Why Does My Window Unit Smell?

Noticing strange odors coming from your window AC unit can be a perplexing and disconcerting experience. These unpleasant odors — ranging from musty to mildewy to hints of exhaust, burning and even rotten egg smells — all demand your serious attention. If you’re noticing any of these weird odors, you need to act accordingly to address them.

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Got a peculiar odor wafting from your treasured cooling appliance? There are several reasons why your window AC unit might be smelling.

Common Window Unit Smells — and What to Do About Them

Musty or Mildewy Smell

Perhaps the most common smell associated with window AC units is a musty smell. It’s probably due to the presence of mold or mildew within the unit. Mold and mildew will grow anytime there’s excess moisture hanging around. When AC units cool the air, they generate condensation, and when that condensation isn’t properly disposed of, it creates the perfect environment for mold and mildew growth.

To fix the problem, check the unit’s drainage system. All too often, the drainage tray and pipe can become clogged with debris. Use a mixture of warm water and vinegar to clear any blockage and kill any mold and mildew in the process.

To prevent moisture-related issues in the future, make sure your window AC unit has proper ventilation. If the humidity is still too high, you can use a dehumidifier in the room to reduce it. Finally, you may want to think about running the air conditioner at a lower temperature in order to limit condensation.

Metallic Smell

A metallic smell from your window AC unit could be a sign of overheating or an electrical problem. Metallic-like smells can emanate from damaged wires or components within the system. That’s why, when you notice a metallic smell, you should immediately shut off and unplug the window unit from its power source. Before operating the AC again, contact a professional HVAC technician to inspect the window unit and make any necessary repairs. Electrical issues can be extremely dangerous and should be addressed as soon as possible to ensure the safety of you and anyone else in your home.

Exhaust Smell

If your window AC unit smells like chemical exhaust, it can be alarming, to say the least. If you're smelling that smell, it’s likely that your unit has a refrigerant leak. Refrigerants have a very distinct odor and typically smell similar to exhaust fumes. Oddly enough, many report refrigerant as smelling slightly sweet, while some report that it can smell similar to a skunk. In any case, refrigerant is harmful to the environment and can cause health issues for those who come in contact with the substance.

A refrigerant leak typically indicates a larger problem within the unit and is often a result of corroded or damaged wiring. If you suspect this might be the issue, turn off and unplug the unit immediately to prevent any further damage or leakage and contact a professional HVAC technician to come take a look at it.

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Burning Smell

Another potentially alarming smell that can come from your window AC unit is a burning smell. Like any other time you smell something burning in your home, it indicates a potential problem that should be taken seriously. A burning smell could be a result of electrical problems like a circuit board malfunction. When this happens, it can cause the overheating of electrical components, giving off a distinct burning odor.

Another reason you may be smelling a burning smell is that the capacitor is broken. The capacitor is the mechanism that powers the fan motor. When the capacitor fails, the motor will overheat, emitting a burning smell. Turn off and unplug your unit as soon as you notice the smell. Then, call a professional HVAC technician to come to assess your unit and make any necessary repairs.

Vinegar Smell

From cleaning to cooking, vinegar is a wonder around the home. That said, it’s not known for its pleasant smell, especially when it’s emanating from your air conditioner. If you smell vinegar coming from your air conditioner, it indicates the presence of bacterial or fungal growth within your unit. This can be due to several situations. For example, a dirty or clogged air filter will restrict airflow in your unit and can quickly lead to bacterial growth. Make sure that you replace or clean your air filter regularly to avoid unnecessary clogs.

Another place where bacterial or fungal growth can occur is in the internal components of the unit. Cleaning the evaporator coil or the condensate tray with a standard household cleaner can help eliminate this microbial growth as well as the unpleasant, vinegary odor.

Also, keep in mind that bacterial growth isn’t always associated with the smell of vinegar. Microbial growth has a variety of associated smells, including a sulphuric rotten egg smell or a musty, mildewy smell as well.

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Reclaiming a Refreshing AC Unit

As great as they can be, window AC units can be puzzling when they start to smell. Knowing what specific smells might indicate can help you understand the root cause of the issue, allowing you to get back up and running before too long. Remember, as you investigate, to always power off and unplug your unit before handling the internal components of the air conditioner. And, when in doubt, always consult your local HVAC technician before making any repairs yourself.