When excess moisture accumulates inside air ducts and vents, it’s caused by high humidity levels or a drainage leak. If you smell something musty as soon as you turn on the AC unit, there’s a chance that mold and mildew have made their way into your ductwork.

Why does my AC make my room smell?

If you smell a moldy odor, chances are that mildew or fungus have begun to grow in or near your air conditioner. This makes sense since air conditioners remove excess moisture from your home in addition to cooling it. When that moisture is unable to drain properly, mold grows easily in areas with remaining moisture.

Why does my house smell like smoke when the AC is on?

Overheated Wiring, Motor or Fan A component of your HVAC system may have overheated. The excess heat may burn insulation on wiring, resulting in a smoky smell. It could also burn any dust or debris on the fan. An overheated motor will also make an odor of smoke; the lubricant on the motor is responsible for the odor.