Common Air Conditioner Smells and What They Mean

The cold air that blows out of your air conditioner may not always smell so nice. While some smells are warning signs for much bigger problems, others are relatively harmless. Here’s an overview of common air conditioner smells, what they mean, and what you can do about them.

Rotten egg smell

A sulfuric rotten egg smell is usually a sign of a natural gas leak. The foul aroma is added by most utility companies in order to help alert homeowners when there’s a leak. A natural gas leak is an emergency situation. If you smell rotten eggs coming from your air vents, there are a few steps you need to take. If the smell isn’t very pronounced, and you suspect the leak is small, open all doors and windows in your home to encourage airflow before contacting your utility company. If the smell is very strong, and you suspect you’re dealing with a larger leak, evacuate yourself and your family from the home. Once you’re somewhere safe, contact your local utility company and report the leak.

Burning or electrical smells

A burning smell could indicate a mechanical problem with your air conditioner’s fan or compressor, issues with wiring, or component failure. But, it can also be fairly harmless. If you notice a burning smell the first few times you turn your air conditioner on for the year, it may just be months of dust burning off. Wait and see if the smell goes away after about 20-30 minutes. If the smell doesn’t go away, contact an HVAC technician for an inspection. Depending on the cause, you may need to get an electrician involved if the problem is with wiring. You may also need to repair or replace your air conditioner if a crucial component is failing.

During an annual air conditioning maintenance visit, our technicians ensure that both the indoor and outdoor unit are free from dust and debris that can cause burning odors and other problems in your home. If it’s been some time since you’ve last turned on your air conditioner, consider having it examined and maintained before you encounter any unwelcome odors or surprises.

Dusty smell

Even in a dry, desert climate, dusty smells shouldn’t make their way indoors. Dusty smells can result from dirty air filters. Along with an unpleasant smell, dirty filters can decrease the overall efficiency of your air conditioner. That’s why we recommend that you replace your filters at least once every three months. If you have pets, or if someone in your home has allergies, it’s best to replace your filters more often—about once a month.

To keep dusty smells at bay, consider upgrading to filters with a higher MERV rating. MERV ratings reflect how effective an air filter is at removing certain categories of airborne particles. A Filter with a MERV rating of 16 or higher is considered a HEPA filter, which provide the highest protection from dust, dander, and more. You can learn more about the ins and outs of MERV ratings, HEPA filters, and all things clean air in our guide to Everything You Need to Know About Air Filters.

Musty or moldy smells

Mold and mildew in your air conditioner can pose health problems to people with respiratory conditions, along with producing less than pleasant smells. The most common causes of musty or moldy smelling air in a home include:

Clogged condensate line

Along with cooling, your air conditioner removes moisture from the air in your home. This moisture filters out of your home and exits through the condensate drain line. This drain is prone to getting clogged with dirt or debris, especially during storms that whip these particles into the air. With nowhere to drain, water can back up and collect in the drain pan, eventually overflowing and creating pools of water around the indoor unit.  Dirty water in a dark place is a one-way trip to mold, and these mold spores can become airborne, causing the air in your home to smell bad.

Dirty evaporator coil

The actual “cooling” in an air conditioner happens along the surface and fins of the evaporator coil. Warm air passes over the coil causing the cold refrigerant moving through it to evaporate. This draws heat (and moisture) from the air, lowering the temperature. The newly cooled air then travels into the ventilation system to various rooms in your home. When the surface of the evaporator coil is mired in dirt, dust, and grime, the coil can freeze over. When it thaws, pools of water will form around the air handler, creating a breeding ground for mold.

Cleaning an evaporator coil isn’t something you should do on your own, as they’re sensitive and easily damaged. It’s best to have a trained HVAC professional clean it for you. As part of our 26-point maintenance plan, we’ll clean your evaporator coil and ensure it’s free from dirt and mold that can impact the air in your home.

Leaking air ducts

Since your air ducts are generally located in an attic, crawlspace, or otherwise out of the way, you might not give much thought to them. That is, until they spring a leak. If your ducts have leaks, mold can grow in the spaces where dust and humid air enter the ductwork. You’ll need a duct sealing and cleaning from a professional in order to address this, since the location of air ducts makes them often difficult, if not impossible, for the average homeowner to access.

Oversized air conditioner

If your air conditioner is too big for your home, it will cycle air throughout your home too quickly, turning on and shutting off several times per hour.  Without completing a full cooling cycle, your air conditioner will not dehumidify the air that flows throughout your home. This leads to excess moisture, and eventually mold, even in dry climates like Arizona. The development of mold can be accelerated by weather conditions, such as Arizona’s annual monsoon season, during which there’s more moisture than normal in the outside air. An oversized air conditioner won’t be able to keep up, leading to a musty, moldy environment.

Many homes have oversized air conditioners—it’s possible yours does too. An oversized air conditioner will likely have a shorter lifespan, costing you more money in the long run due to needing more frequent repairs. A properly sized air conditioner will take into account factors like square footage, the direction your home faces, the state of your windows and doors, and more. That way, you’ll have clean, cool, dehumidified air with no risk of mold or mildew.

Strange smells? Contact Chas Roberts

No ifs, ands, or buts about it—your air conditioner shouldn’t smell bad. If you can’t take a deep breath in your home without cringing at a foul odor, it’s time to call in the experts. No matter the problem, we can diagnose it and solve it with ease. After all, we’ve been helping families throughout the Valley with all their HVAC needs for over 75 years. Contact us to get started.