Nine Weird AC Smells and What They Mean

Air conditioning is a necessary part of modern life, especially during the hot summer months. When you run the air conditioner, you expect nice, cool, refreshing air to enter your home. But sometimes, AC units give off weird or concerning odors that make you wonder if something’s wrong. 

A strange smell coming from your AC unit or ductwork might be no big deal — or it could signal a serious problem requiring immediate attention. When in doubt, turn off the unit and call an HVAC technician to take a look. In the meantime, learn about nine weird AC smells and what they might mean. 

1. Rotten Eggs 

A rotten egg smell could point to a gas leak in your HVAC system. Air conditioners don’t run on natural gas, but they share a blower and ductwork with gas-fired furnaces, which could be the real culprit for this smell. If you notice a rotten egg smell coming from the vents, turn off your air conditioner immediately, open the windows for ventilation and evacuate the house. Then, call an HVAC contractor right away to check for a gas leak and perform the necessary repairs. 

2. Musty Odors 

A musty smell usually indicates mold or mildew growth inside the AC unit or ductwork. These microorganisms thrive in damp, dark environments, making the evaporator coil and air filter common places for mold to set in. To get rid of the musty smell and prevent further mold growth, hire a professional to clean your air conditioner, replace the filter and identify any other sources of moisture. 

3. Cigarette Smoke 

If someone in your home smokes, chances are the AC will start smelling like stale cigarettes before long. The buildup of nicotine and other chemicals inside the unit, air filter and ductwork circulates into your home every time the air conditioner runs. Change the filter regularly and schedule routine maintenance to help prevent this AC odor. Also, it would be wise to not smoke inside the house. 

4. Sewage 

If you detect a sewage smell from your air conditioner, your plumbing or sewer system could have a problem. The smell may be caused by methane gas emitting from a broken or clogged sewer pipe or a dry drain trap, which has found its way into the ductwork. Methane is dangerous, so if you smell a sewage-like AC odor, contact a plumber without delay. 

5. Stinky Feet 

A dirty air conditioner with a buildup of bacteria and fungi can emit a smell reminiscent of dirty socks. This odor may be particularly strong when you turn on the AC for the first time in the spring. Regular cleaning and maintenance helps prevent this odor from occurring. 

6. Skunk Smell 

If you smell a skunk-like odor coming from your AC unit, there may be a dead animal or animal waste inside the ductwork. It’s possible a sick or injured bird, rodent or other pest climbed inside an air duct during the winter, where it died and began decomposing. This is a health hazard, so reach out to an HVAC technician to address the problem. 

7. Electrical Burning or Gun Powder 

If your AC emits a burning smell, it’s likely due to an electrical issue, such as a damaged motor, circuit board, compressor or wiring. If any of these components overheat, they may emit a burnt, gun powder-like smell. To prevent permanent damage, turn off the AC immediately and call an HVAC technician to diagnose and fix the issue. 

8. Car Exhaust 

A smell similar to car exhaust could signify a refrigerant leak. Refrigerant is the chemical your air conditioner uses to extract heat from the indoor air and exhaust it outside. A leak can be a serious health and environmental hazard, so turn off your cooling system and call for help. 

9. Chemical Fumes 

A chemical-like smell coming from your air vents could be traced to nearby vehicles, cleaning products, paints, adhesives or other substances. If your AC blower fan motor is situated in the garage, even a car’s idling exhaust could mingle with the indoor air. These are serious concerns that could warrant sealing the ductwork or even redesigning your HVAC system. 

Schedule Air Conditioning Repair 

If you’re concerned about a weird smell coming from your air conditioner, turn to Service Experts Heating, Air Conditioning & Plumbing for the repair you need. We use advanced diagnostic equipment to quickly and accurately determine the problem. Then, we’ll explain the most cost-effective repair methods and offer recommendations to prevent a recurrence. We believe in our excellent work so much that we back every repair with a one-year 100% satisfaction guarantee! Contact a Service Experts office near you for more information or to request air conditioning repair in the U.S..