What to Do When Your Window Air Conditioner Smells

updated Jul 24, 2021
We independently select these products—if you buy from one of our links, we may earn a commission. All prices were accurate at the time of publishing.
Woman is checking to see if the air conditioner is cooling. She is holding the remote to the air conditioner and raised her hand to check temperature.
Credit: Getty Images/ Aja Koska

A smelly air conditioner unit is nothing short of gross. But what can cause these exhaust fumes, or gunmetal, musty/mildew-y, burning… (need we go on?) scents? And better yet, how can you get rid of them? After all, you install your air conditioner to cool down the air in your home, not stink it up with unpleasant odors, some of which might even be potentially dangerous. 

Here’s what you need to know about a variety of scents that may be wafting out of your window AC unit, as well as tips on how to maintain your AC so that these problems don’t develop to begin with. 

Exhaust fume smell

What causes the smell: This may mean there’s a leak in your refrigerant line, which releases chemicals into the air, according to Cielo, an AC unit retailer. If you smell this, turn the unit off immediately, and open windows to ventilate your space. This can be dangerous, so speak to a professional before you try using the unit again.

Gunmetal odor

What causes the smell: This scent can happen if your unit’s fan motor or circuit board is shorted out, according to Air Experts, an air conditioning installation, repair, and maintenance company. Be sure to shut off your AC unit if you smell this.

Musty/mildew-y smell

What causes the smell: Moisture can collect in your system and foster microbial growth, according to Service Champions, an AC service, repair, and installation company. 

Burning stench

What causes the smell: This may mean that you haven’t turned the unit on in a while and dust has settled inside it, according to Cielo. Once you turn the unit on, the dust burns, causing a temporary smell, but this is nothing to worry about. However, it could also indicate something more serious: A lingering burning smell might mean something within your AC unit is actually burning, at which point you’ll want to turn the unit off until it’s fixed. 

How to get rid of AC smells

In most cases, this is no DIY project. Make sure to consult with a professional. You can check the average price of an AC unit repair on HomeAdvisor, and book a pro you trust there as well. 

A good pro should be able to advise whether the cost of repair is more or less expensive than the unit itself. If you want to stay mindful of your waste, it could be worth putting in the money to repair your existing unit, but if the cost is way more than what you paid for your unit, you might want to look into purchasing a new unit — especially if your window AC unit is 10 to 15 years old.

What to do for maintenance

Here are some things you can do to maintain your AC unit so none of the above occurs to begin with: 

  • Replace or clean its filter regularly. This can lower your unit’s energy consumption. When dust enters the evaporator coil, it impairs the coil’s heat-absorbing capacity, according to energy.gov. You can use a vacuum to gather lint off your filter and then wash it with warm, soapy water to clean it, according to CNET. Just make sure it’s totally dry before returning it into your AC unit. 
  • Clean the unit. Dust can gather on the outside of your unit too, which will just end up being blown throughout your home.