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My Air Conditioner Smells! Why and How Do I Get Rid of The Smells?

The short answer is: The unit is not properly ventilated and the coils are dirty. This can cause a musty smell to build up over time. Another possible reason is that there is mold or mildew growing inside the unit.

Is there an unpleasant smell in your house that seems to get worse as soon as your air conditioner runs? While you will want to find the reason and eliminate the smell ASAP, you may not be aware that it can also cause serious health hazards.

So, let's go over the nine most common reasons why an air conditioner smells terrible and the solutions you can take to eradicate it. Different smells can mean different things, from musty smells to stale cigarette smoke to a locker room smell to a rotten egg odor. Learn more about solving your smelly air conditioner problems.

The Central Air Conditioner Smells Like...

1) Car Exhaust Fumes Smell

AC units don't have an engine like a car. Which means there's no explanation for your home air conditioner smelling like a car exhaust. However, your AC system does make use of some liquids and fluids, and when they're heated, they do have the tendency to smell like car exhaust fumes.

And this particular smell can typically mean that the air conditioning system in your home has some refrigerant leak. The refrigerant is a cooling agent inside your AC, and if it leaks it can impact the performance of the air conditioner. It can also release chemicals into the air and cause harm to the environment.

Freon is a chlorofluorocarbon, and it was commonly used as a refrigerant in air conditioners. Although now slowly being worked out, freon takes on heat from the air indoors and releases it outside.

This can also be hazardous to the environment, which means (if freon refrigerant is used in your air conditioner) you should take extra care if you notice a freon smell and there is a leak.

2) Burning Smell

An air conditioner has lots of electrical components within it. If you can detect burning plastic smells from your AC unit, it most likely means that one or multiple parts of the system are actually burning. In this instance, make sure you turn off your HVAC system immediately and contact your local AC repair company.

An air conditioner burning smell can also be due to dust settling within HVAC systems after not being used for a long period. When an AC unit hasn't been used for this amount of time, it can cause the dust to burn, therefore producing unpleasant air conditioner smells. 

If the burning plastic smell remains or returns and the system begins to malfunction, make sure you turn off your unit and contact your HVAC technician or gas company immediately. If it gets worse, you'll want to call the fire department.

Burning rubber smells can also indicate another problem — specifically a broken fan belt. If you sense this smell, you'll need to contact your HVAC company as soon as possible, too.

3) Rotten Eggs Smell

Homeowners - if you smell rotten eggs in your home, never ignore it, because what you are smelling is a gas leak. Sulfur, in particular.

And while natural gas is actually odorless, manufacturers are required to add mercaptan - a chemical - in order to give it the distinctive rotten egg scent to identify a natural gas leak.

If you are unfortunate enough to get a gas smell like this through your air ducts, remember these points:

  • Don't operate anything electrical.

  • Don't use lighters or matches.

  • If you have any candles lit or open flames, put them out.

  • Open as many windows and doors as possible.

  • Turn off the gas supply at its meter. If you can't do it at home, your gas firm will do it for you.

  • Evacuate the building promptly.

  • Don't turn the gas back on. Your company will do that for you when it's safe.

A rotten smell can also be caused by a dead animal becoming stuck in your air conditioner. Birds and insects can nest in these small spaces and often get trapped, causing the bad central air conditioner smells.

4) Moldy and Musty AC Smell

A stale and musty smell is one of the most common air conditioner smells. If your AC smells like this, generally, it's caused by an accumulation of water in the drain line and drainage system. This drain line problem can cause mildew, mold, and fungus growth.

A moldy air conditioner smell can also be caused by a dirty air filter. For example, if you live in a hot and humid climate and you turn on your air conditioning unit after a long period of time, moisture can develop in the filters, requiring a new air filter.

Also, you may have heard of dirty sock syndrome. This is when mold and mildew-like odors (that smell like dirty socks) seep from your air conditioner when you first turn it on. Caused by moisture, dirt, and dust build-up, if not addressed, bacteria can multiply.

Preventing dirty sock syndrome will require your heating and cooling company to get your refrigerant lines and ducts appropriately cleaned, as well as locate the source of the problem.

5) Cigarette Smoke

If you smoke in your house, you'll find that your air conditioner will eventually end up smelling like it. This cigarette bacteria buildup can cause this smell, which can eventually lead to headaches and allergic reactions due to poor indoor air quality.

An evaporator coil and filter absorb these cigarette fumes, and once you turn on your air conditioner, the tobacco particles become loose and end up being redistributed throughout your house. 

You'll need an evaporator coil clean to remove this smell, as well as a filter change every 30 to 60 days.

6) Vinegar Smell

If you detect a vinegar odor, it could be to do with an electric motor problem that is emitting ozone. Other possible reasons could be a malfunctioning filter, mold in the ductwork, condensation in the coils, or a clogged condensate pan. This is a problem for your indoor air quality and the ozone layer.

You can typically resolve this issue easily by purchasing cleaning products for air conditioning. The enzymes within the products remove the common air conditioner smells almost straight away, and prevent them from coming back.

7) Sewage Smell

Dry P-traps allow sewer gases to back up into your home. Once a month, turn on all your sinks to run water and fill up your P-trap. This will create a seal against future sewage scents.

If the dry P-traps aren't the issue, it may be because you have a ruptured sewer vent pipe. It could also be a backed-up sewer line. Sewer gases can be incredibly dangerous, so it's imperative you contact your HVAC professional to take a look at your cooling and heating systems.

8) Skunk Smell from Central

When an air conditioner smells like skunk, it usually means there's a refrigerant leak. It's usually methyl mercaptan - a gas that makes the air conditioner smell specifically like a skunk's spray. When this gets into your ductwork, it can be dangerous.

If your air conditioner smells like this, it's recommended you evacuate your house immediately before contacting your HVAC company.

9) Sweet, Chemical Smell

Sweet, chemical smells also indicate a refrigerant leak. Your HVAC system relies on the gas to shift heat through the copper coils, which, as time passes, can break down. This type of refrigerant leak calls for expert attention, too.

How Do I Get Rid of the Smell in My Air Conditioner?

You want to know "why is there a smell coming from my air conditioner?". But before you conduct a full investigation, here's what you can do.

Shut down all the electricity. Maintenance begins in safety. When using an air conditioner in a residential home, you must turn it down to its source. Then, change the filter, clean the cylinder and clean out condensation lines.

Contact Us at ARS/Rescue Rooter for Better AC and Indoor Air Quality

If you hear unexpected air conditioner noises or the air conditioner smells bad, it's time to call ARS/Rescue Rooter. Our professional team will get your AC system back in shape and keep you and your family safe.

Find your nearest location and give us a call today and learn how we can help.

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