Why Your Car's A/C Smells Bad (And What You Can Do To Fix It)

For travelers, there are few things more frustrating to contend with while driving in the spring and summer months than an air conditioning unit that isn't blowing cold air. Even worse is if you've turned it on and noticed that your A/C has started to let loose a foul odor, which could indicate several problems. 

Understanding why your A/C is giving off a particular smell is crucial to protecting the health of both you and your car. Some odors point towards internal issues with your vehicle that might require professionals to tackle. Breathing others in for an extended period of time can wreak havoc on your respiratory system and cause other health problems. But among the many tips and tricks that will save you a mechanic trip is a way to combat the A/C smell on your own. Thankfully, it's not especially difficult, with the process only requiring some simple steps and materials. 

Before trying to get rid of the smell coming from your car's A/C unit, it's worth understanding why it's happening, as different aromas point to different issues.  It's not uncommon for mildew and mold smells to make their way from your A/C unit, especially for those residing in humid environments. This is often caused by moisture building up in the A/C evaporator over time, resulting in the formation of bacteria. Dust particles can also block the evaporator and cause mold buildup. Similarly, a vinegar-like scent can also be attributed to different kinds of mold along with other potential problems such as a leaking car battery, refrigerant leakage, or strong ozone emissions. 

While some of these scents can potentially be eliminated on your own, others are a telltale sign that you'll need professional help. The scent of burning may point to severe problems with your A/C compressor or even electrical shortages. Likewise, the smell of an oil or gas leak will eventually seep through your A/C filter and make themselves readily known. Even a sweet scent coming from your A/C can be cause for concern, as this can be a sign of an antifreeze leak taking place in your system. 

Before trying to remedy your car's strange scent, double-check the condition of your A/C evaporator. Leave your A/C on for a while and check if condensation from under the windshield is dripping or if the front passenger footwell carpet is somewhat damp. If neither is occurring, then you know there's an issue.

You'll first need to purchase a new cabin filter for your car if it uses one — or try out a more economical method to do so – and a can of spray disinfectant made especially for car A/C systems, which are available in most auto part stores. With everything at hand, follow these steps:

1. Start your engine and roll the windows down to avoid breathing in any disinfectant. 
2. Leave your A/C off, but turn the temperature to full cold and choose Vent mode. 
3. Have your fan blast on high for a few minutes to try drying out moisture. 
4. Leave the engine on, turn the temperature to full heat, choose Heat, and blast the fan on high for a few minutes. 
5. Take out your car's cabin filter if it has one, which may require a mechanic's aid. The task is unlikely to be successful without removing this. 
6. Turn the fan on high with the A/C on and note if the smell is present. 
7. Locate your air intake vents by placing a piece of tissue paper or your hands over the grilles. They may be outside on the windshield base or under the hood. 
8. Spray the disinfectant into the intake vents for about 30 seconds and keep the A/C running. 

If the smell persists, it can mean an even more intense cleaning is required. If you're not comfortable accessing the hard-to-reach evaporator, bring your vehicle to a mechanic.