Nine Weird AC Odors and What They Mean

Air conditioning is an important 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 nothing to worry about — 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 indicate 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 true 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. After that, call an HVAC contractor at once to inspect 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 prevalent places for mold to take hold. To get rid of the musty smell and prevent further mold growth, hire a specialist 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 accumulation of nicotine and other chemicals inside the unit, air filter and ductwork circulates into your home every time the air conditioner operates. 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 perceive 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 stench, 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 notably strong when you turn on the AC for the first time in the spring. Regular cleaning and maintenance helps prevent this odor from happening. 

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 compromised motor, circuit board, compressor or wiring. If any of these elements overheat, they may emit a burnt, gun powder-like smell. To protect against 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 indicate a refrigerant leak. Refrigerant is the chemical your air conditioner uses to pull 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 products. 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 call for sealing the ductwork or even redesigning your HVAC system. 

Schedule Air Conditioning Repair 

If you’re worried about a weird smell originating from your air conditioner, turn to Strogen's Service Experts for the repair you need. We use advanced diagnostic equipment to quickly and accurately determine the problem. Then, we’ll share 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 Rochester.