Odd Air Conditioning Smells and What They Mean

There is nothing more jarring than being woken up in the wee hours of the morning by the smell of something burning. It is an added blow to the gut (and to the wallet) when the realization strikes that said smell is coming from your air conditioner. Fortunately, not all smells are as worrisome as others. Odors can be broken up into two main groups: common run-of-the-mill culprits and causes of concern.

Common Culprits 


The most common A/C odor is the smell of mildew. If your A/C unit has not properly drained the moisture in the air that it has collected, mold or mildew can begin to grow. Sometimes, it is as simple as a dirty filter that needs to be replaced. If the smell lingers, a good A/C cleaning by a professional should get rid of the smell.


Once again, water is the ultimate culprit. If water inside the A/C unit becomes stagnant, you may notice a faint foot odor that lingers in the air. Cleaning your unit and repairing the unit so that water is able to properly drain should take care of that odor.


Your A/C unit’s evaporator coil is a magnet for cigarette smoke. Every time you run your A/C system, the old odor is released through the coil. A quick clean of the evaporator coil should remedy this issue.


A rotting garbage smell is certainly the most unpleasant of the four common culprits because the smell is typically the result of a dead animal. It’s best to call an HVAC technician to come out and rid your air ducts of the animal.

Causes of Concern


A burning smell usually means that you have a mechanical issue on your hands. Turn your unit off immediately and call a tech right away.

Rotten Eggs

If your A/C vent starts emitting the smell of rotten eggs, leave your home at once. Call your gas company before calling an HVAC tech as this is likely due to a gas leak.


This is another smell that may indicate a very large problem such as a backed-up sewer line. A plumber and an HVAC technician should be your two points of contact.

If you’ve started to notice an odd smell coming from your air conditioning unit, Contact the experts at Cascade or Call (509) 642-6383. Available 24/7, Cascade Mechanical will tend to your needs at any time of day.