June 4, 2025
If you’ve ever turned on your AC and noticed a musty smell from it drifting through your home, you’re not alone. That weird, mildew-y scent is more common than you think, and it’s not something to ignore. A musty smell from the AC unit can be more than unpleasant; it’s often a sign that something deeper is going on inside your system.
Here’s what might be causing it, and how to clear the air.
When your AC smells musty, the most common culprit is mold or mildew growth inside the system. Your air conditioner pulls moisture from the air, and if that moisture doesn’t drain properly, it can linger in the drip pan or ductwork, creating the perfect environment for mold.
You might notice the AC smells like mildew especially when it first turns on after being idle for a while (Like at the start of summer). That initial burst of stale-smelling air is often your system clearing out built-up condensation or dust.
Here are some of the most common reasons your AC unit smells musty:
If your AC smells moldy, start with a few simple steps:
Once you’ve cleared out the smell, here’s how to keep it from coming back:
A musty smell from your AC unit isn’t something you have to live with. If your HVAC smells musty, it’s your system’s way of asking for help. Whether it’s a quick filter change or something more involved, dealing with it early can prevent bigger issues and keep your home from smelling fresh.
Need help figuring it out? Our licensed techs can take a look, clean your system, and make sure everything’s working (and smelling) the way it should with our MintCare maintenance plan.
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