Why does my A/C smell, and how can I fix it?

Why does my A/C smell, and how can I fix it?






Air conditioning is the key to a comfortable home, especially in warmer climates and summer months. Imagine coming home on a hot summer day and turning on the air conditioner. Just as you’re ready to enjoy the cool air, a terrible smell hits you. Is the A/C broken? Is there something in the ducts? How do you get it to stop? 

Thankfully, there are steps to get your air conditioning smelling fresh again. We also recommend routine maintenance on your air conditioner to keep it from smelling bad in the future. Let’s walk through some of the probable causes of that odor from your A/C and what you can do to remove and prevent it from happening again.



What is causing my A/C unit to smell?


There are many possible reasons why your air conditioner smells bad, from mold and mildew to electrical issues or dead animals. Don't worry; these smells don’t always mean you need an A/C repair. Air conditioner smells are common and can be fixed with a bit of A/C maintenance and cleaning. Here are a few of the most common smells and how to determine what to do next.

Burning smell coming from the A/C unit

There are two possible reasons if you smell burning when you turn on the A/C. It is likely dust if the smell goes away after a few minutes. After sitting for a long period, dust can settle inside and burn up once the unit turns on. Keeping your A/C free of dust can help prevent this issue.

It is likely an electrical issue if the smell persists or smells of burning plastic or gunpowder. Turn off the unit immediately. Air-conditioner units contain everything from circuit boards to fan motors to compressors. Parts can overheat or get stuck, especially if the unit (A/C or HVAC) hasn’t run in months. Call a professional when this happens. Do not perform your own maintenance. 

Exhaust or chemical smell coming from the A/C unit

If the A/C smells like exhaust fumes, the refrigerant line is likely the culprit. This smell indicates a leak in the coolant line. Turn off the A/C and ventilate the home so you don’t breathe in any chemicals. 

Older A/C units use Freon, a hazardous coolant chemical. If there is a refrigerant issue, there could also be a Freon leak. Freon has a sweet aroma, but don’t rely on the smell to know if there is a leak. Ask your HVAC professional to check for Freon leaks. Take precautions even if you are unsure if your air conditioner uses Freon. Turn off your unit and ventilate your home.

Mold and mildew smell coming from the A/C unit

A mold and mildew smell can only mean one thing: water. Air conditioners pull humidity out of the air as it cools, creating condensation. This moisture causes issues around the evaporator coil, drain line and drain pan if it doesn’t evaporate. Mold and mildew can build up if these areas don’t dry out.

Condensation also can cause mold and mildew growth in the air ducts. Removing mold and mildew from the air ducts is best done by a professional to ensure cleanliness.

Mold and mildew gathering inside your air ducts can lead to various health concerns. When the A/C unit is on, it can blow harmful air particles throughout the home. Mold exposure can cause respiratory issues, especially in those who suffer from allergies and asthma.

Check your air filters if you use a ductless unit. Mold and mildew love to hide in the air filter whether you have a ductless system or not. Excess moisture can gather there when the unit is off, especially if you live in a humid climate.

Dirty sock smell coming from the A/C unit

If your A/C smells like dirty socks, there is probably an issue with the evaporator coil. Mold and mildew could have grown around the coil, causing dirty sock syndrome. This condition frequently occurs in areas with high humidity or where the temperature changes from hot to cold quickly. 

A/C units pull humidity from the air. Moisture can become trapped inside the unit because of the quick temperature change, allowing bacteria and mold to grow on dusty coils. Luckily, a simple cleaning by an HVAC professional can fix dirty sock syndrome.

Skunk or gas smell coming from the A/C unit

A nasty skunk smell could actually save you from a disaster. If you smell skunk or sulfur coming from your A/C, you likely have a natural gas leak within the system. While natural gas is odorless, companies add methyl mercaptan to the gas as a safety measure to give it a nasty smell in the event of a leak. If your A/C smells like skunk, immediately turn off your gas supply and call your utility company.

Natural gas is highly flammable. To ensure your and your family’s safety, avoid sparks and open flames. Open windows for ventilation and exit the building. While low levels of natural gas aren’t hazardous, high levels can lead to loss of consciousness or other serious side effects. Follow all instructions given by your local gas company.

Rotten-egg smell coming from the A/C unit

A rotten-egg smell usually means a dead animal is in your unit or air ducts. Sometimes wild animals or rodents find shelter in your ducts during winter. Birds can make nests inside or on top of units. Many of these animals die, decompose and cause your unit to smell. Dead animals can also damage your unit. Call a professional to remove the carcass from the unit, check your air ducts, and ensure everything is clean before use.



How can I avoid bad smells from my air conditioner?


Before turning on your A/C unit this year, you can take a few steps to prevent your unit from exuding a foul smell.

Inspect the unit for insects or animals

To avoid the smell of rotten eggs, inspect your A/C units and air ducts. Clean out any bird nests, debris or insects that might have gathered over the cooler months. Open any user maintenance sections, such as the filter space, and check that they are clear. 

Peek into your air ducts as far as you can to ensure nothing has made a winter home inside. While it can be challenging to check the entire duct system, you can check easy access points. You can also speak with an HVAC technician about ways to prevent animals from crawling inside your air ducts in the future.

Clean the unit and air ducts

After inspecting your unit and ducts, clean them to the best of your ability using a damp cloth and cleaning agent of your choice. Call a professional HVAC technician for an air duct cleaning if you cannot reach an area. They will ensure there isn’t any lingering mold or mildew inside the ducts that could cause a musty smell. Cleaning the air ducts can also improve overall airflow and air quality throughout the home.

Replace the air filters

Whether your A/C smells or not, changing the air filters will help improve indoor air quality. Air filters keep dust and allergens from spreading throughout the home. Changing them regularly will also prevent moisture from condensing inside. It’s recommended to replace air filters every 90 days. 

When do I need to contact a professional?

Immediately call a professional if your A/C smells like burning plastic, car exhaust or skunk spray. Electrical issues cause burning smells, so do not attempt to fix them yourself. Similarly, if your air conditioner smells like exhaust, your unit could be leaking potentially dangerous chemicals. Keep the unit off and ventilate the home until a professional HVAC contractor can assess the situation.

When your air conditioner smells like skunk, there are two steps you need to take immediately. First, turn off your gas supply and A/C unit. Second, call your local gas utility. It will help find the gas leak, which should stop your A/C from smelling and keep you safe.

Contacting a professional isn’t limited to dangerous situations, however. If your A/C smells like mildew, a professional can help ensure your drain line, condenser and drip pan are working correctly. Consider calling a professional to clean the air ducts even if your A/C doesn’t smell, especially if it has been a few years.



Is my A/C unit breaking?


Are you concerned that a weird smell could signify your A/C is breaking? Don't worry; smells aren’t always a sign that you need a new A/C or HVAC system. 

However, there are a few signs that a replacement might be necessary. Here are a few things to keep an eye out for: 

  • Warm air coming out of the vents
  • Little to no air coming out of the vents
  • High humidity
  • Coolant or water leaks
  • Frequent cycling or other unusual noises

Contact a professional if any of these issues persist, or consider a replacement.



Get your air conditioning covered with a Cinch home warranty plan


No matter the air-conditioning issue, Cinch Home Services helps make home ownership easier. Our Built-in Systems plan covers your home’s air-conditioning unit and ductwork, meaning you have covered service for your A/C system. 

Even if you are new to the home, we don’t hold pre-existing conditions against you. We even offer a $25 credit toward new filters for your A/C or fridge. 

Don’t wait; get a quote now and join the nearly 1 million other homeowners who already use and trust Cinch.



Learn why your A/C smells bad, how to deodorize your air conditioner and how to avoid unpleasant odors.

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