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Most homeowners don’t think too much about their HVAC system until something is wrong with it. You likely use it almost every day, especially during hot summer days or chilly winter nights. Any system is bound to run into issues and problems as it grows older, and an AC system is no exception. You might be wondering why your AC starts to smell when you turn it on. Listed below are a number of different reasons why your AC might smell strange when you first turn it on.


The indoor unit and cooling coils are a perfect place for biological growth. It’s cold and damp. AC units are not only designed to take the air and cool it to a comfortable level, but they’re also designed in such a way to help directly remove moisture from the air. If it’s not efficiently draining the captured moisture, then it creates a welcoming environment for mold and mildew to form. In addition, having a dirty filter can also cause the smelly odor of mildew to waft up from the register vents and be smelled throughout the home.

Dead Animal

Every once in a while, a small animal can squeeze its way into the air ducts or AC system. Injured or sick birds or rodents may have been able to get into the small, confined space of the AC unit or ducts. When the entire system is turned on for the first time, it spreads the odor throughout the entire home. The smell can often be unbearable, and you’ll need to hide a professional to clean out all of the ducts to ensure that all the rodent remains are properly and completely removed.

Backed Up or Ruptured Sewer Pipes

If you smell a whiff of sewage, you might be smelling the aftermath of a backed-up sewer line or a ruptured vent pipe that’s near the AC system. An improperly run condensation drain can cause sewer gasses to enter the AC system.

The odor you may be smelling is methane gas, which is an incredibly dangerous gas to have seeped through your home. If this is something you smell, you should evacuate the home for safety and immediately call an HVAC team to examine the situation.

Shorted Out Motors and Circuit Boards

On occasion, a fan or circuit board will short-circuit, causing your home to begin smelling like gunpowder. Although this may only be prevalent when you first turn the system on, it is an important smell to be aware of. If you smell the odor of gunpowder, call your AC technician today to schedule an appointment. They will be able to help you identify any broken parts and can recommend replacement components.

If you smell something strange in your AC unit, give us a call today at Comfort Experts. Some smells may be harmless but others can be incredibly dangerous. If you smell something particularly awful or odd, give us a call immediately and we’ll be able to help you identify the cause of the smell. In some cases, it’s wise to get out of the home before you make the call, just in case you are smelling a dangerous gas that is harmful to you and your family. Play it safe and give us a call today!

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