A/C bad smell

When it’s 95° outside and sweltering inside your home, the last thing you want is to encounter a foul smell when you turn on your A/C. No family should have to choose between being uncomfortable in their own home or being forced to breathe in nauseating smell. 

Are the gross smells coming from your A/C normal? If so, where are they coming from, and how can you prevent them in the future? 

These are all questions we've been asked before, and we know it can be extremely frustrating to be faced with a foul-smelling A/C. Here are the three main reasons your A/C is emitting a funky smell: 

Condensation and Mold Growth

Your air conditioner can sometimes create internal condensation, which forms when there is a significant temperature difference between the A/C housing and the air outside.

When moisture collects in your A/C, mold can start to grow. Debris, insect shells, and dust can also start to gather and stick to the condensation inside the unit. After a while, this combination of mold and debris can create an unpleasant smell that is distributed throughout your home when the A/C is turned on.

Dirty Air Filter

When was the last time you changed your air filter? If it's been a while, the filter has likely collected nasty particles from the air. When your A/C filter is dirty and clogged, the cold air from your system is forced to push its way past all the unpleasant contaminants before being dispersed throughout your home.

Dirty Ducts

In a similar fashion, your duct system can acquire mold, bacteria, dust, dirt, and debris over time. If it's been a while since you've had your ducts cleaned (or if you've NEVER had them cleaned), the foul smell coming from your A/C could actually be originating in your ductwork. 

When cold air comes out of your A/C, it flows through your duct system before being distributed throughout your home. Your ducts serve as a sort of superhighway for your home. After a while, any bad smells coming from your ducts will be in every corner of your home. 


Luckily, solving a bad smell coming from your A/C is easy. Whatever is creating the odor simply needs to be cleaned. If it's an issue with your ducts, schedule a duct cleaning. If your furnace filter is clogged, replace it. 

Mostly importantly, keep your A/C unit clean by scheduling yearly maintenance. A typical A/C tune-up will include the cleaning of your unit's parts, so make sure to get your A/C checked out this season. If you're in the Chicagoland area, Four Seasons is available 24/7 to help you with all your A/C needs.