May 12, 2014

On a hot day, the first thing you do when you return to a warm, stuffy home is switch on the air conditioner to circulate some cool air. However, there is nothing relaxing or comfortable about cool air carrying a strong odor that eventually spreads throughout your home. If you ever find yourself asking “why does my air conditioner smell?” then find the odor that best matches yours below.

Common Odors

First, be certain that the smell is coming from your air conditioning vents and that the source of the foul odor isn’t something else, such as an overflowing garbage can or burned macaroni and cheese on the stove. Second, check the air conditioning filter. If it is dirty and clogged, it may not be filtering properly and may be contributing to the problem. Cleaning or changing the filter might not only solve the stinky issue, but it will also help your air conditioner more efficiently and effectively cool your home.

If that doesn’t solve the problem, a number of common smells that may emanate from your vents could be the sign of a larger issue. Some are more offensive than others, but if any persist, it might be a sign of trouble for your central air conditioning unit. The following three scents are most common odors that people encounter:

  • Mustiness – If there is a persistent musty smell, there are a few possibilities for the source. First, mold or mildew may have grown on the condenser coil inside the AC unit if there is a problem with moisture or drainage. There could also be mold or mildew growing in the ductwork if there is a leak in a duct. Whatever the source, when the air flows through the vents, it spreads mold spores throughout your home, which is unhealthy and can cause intense allergic reactions. In cases like this, the condenser coil can be cleaned, drainage lines can be inspected, drain pans can be emptied, and the ductwork can be checked for possible leaks and mold or mildew growth.
  • Rotten eggs – If the air pouring from your vents smells a little like rotten eggs, you might have a natural gas leak. Many AC units are part of a complete system that also houses a furnace or heat pump, which may be fueled by natural gas. A natural gas leak is quite serious and you would need to immediately turn off the unit and open windows to air out your home. You also would have to call the gas company and an HVAC professional so you could cut off the gas and repair the malfunction.
  • Burning or smoke – If someone in your home smokes a lot, sometimes the smoke can be pulled into the condenser coil. Just like mold, once that smoky smell permeates the coil, it will contaminate the air blowing into your house. Now, if it smells as if something is actually burning, there might be a mechanical problem with the AC unit’s fan or compressor. Check the central air conditioning unit to see if you smell anything burning around the actual unit. If it is burning, then turn off the unit immediately to prevent further damage or fire, and call an HVAC professional.


It is imperative that you maintain a clean air filter for your AC unit. Make sure that it is not clogged, dirty, or damp, and change it even if it hasn’t lasted as long as the manufacturer suggested. Depending on factors in the home, such as pet hair and cigarette smoke, you may need to change the filter more often than recommended by manufacturers. There are also several types of filters that screen more than just dust, including allergens (pet dander, dust mites, mold spores) and odors (pet odors, cigarette smoke). Such filters are available at home improvement stores or in home improvement departments and prices vary.

Regular maintenance of your AC unit will also help prevent these odors from occurring. When you have an annual inspection, an HVAC specialist will tune-up your central air conditioner and be able to catch little problems before they turn into big, expensive ones. Yearly maintenance will extend the life of your central air conditioning unit.

If you have noticed any of these odors, please contact Comfort Pro, Inc. today for an appointment so that an HVAC professional can determine the source of the smell and find a remedy for the problem.

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