If you’ve noticed a musty or mildew-like smell coming from your car’s air conditioning shortly after replacing struts or even while driving over rough roads it might not be a coincidence. A failing strut top mount can indirectly lead to that unpleasant AC odor by allowing excess moisture and debris into areas where mold and bacteria thrive. While it sounds unusual, the connection between suspension components and cabin air quality is more common than many drivers realize.

How can a strut top mount cause AC odor?

Strut top mounts sit at the top of your vehicle’s suspension struts, connecting them to the body. They absorb vibrations and help isolate road noise. When these mounts wear out or crack, they can create small gaps near the firewall the wall separating the engine bay from the passenger cabin. These gaps may let in rainwater, road spray, or humid air that shouldn’t be there.

That extra moisture often ends up near the HVAC system’s air intake, which is typically located at the base of the windshield. If water pools around this area or seeps into the cabin air filter housing, it creates the perfect environment for mold and mildew to grow. Once the AC runs, it pulls that damp, contaminated air into the cabin resulting in that familiar musty smell.

When does this usually happen?

This issue tends to show up under specific conditions:

• After recent strut or suspension work, especially if seals weren’t properly reinstalled
• During or after heavy rain, when water finds its way through compromised mounts
• When driving on wet or muddy roads frequently
• If you already have a clogged or old cabin air filter that traps moisture

Sometimes, the odor appears only when the AC is turned on, or it worsens after hitting bumps clues that vibration or movement is letting air (and moisture) through a faulty seal.

Common mistakes people make

Many drivers assume the smell is just a dirty cabin filter or a need for an AC system cleaning. While those can be contributing factors, ignoring the suspension side of the problem means the odor will likely return. For example:

• Replacing the cabin air filter without checking for water intrusion points
• Using odor-eliminating sprays that mask but don’t fix the root cause
• Assuming new struts mean everything is sealed correctly when in fact, worn top mounts may have been reused

In some cases, mechanics replace struts but leave old top mounts in place because they “still look okay.” Over time, those aged rubber components lose their sealing ability, even if they haven’t fully collapsed.

What to check first

Start by inspecting the area around your strut towers under the hood. Look for signs of water stains, dirt buildup, or cracked rubber near the top mounts. Also check your cabin air filter if it’s damp, discolored, or smells musty, that’s a strong indicator moisture is getting in from outside.

If you recently had struts replaced and now notice a smell, review what was actually replaced. Ask your shop whether the top mounts were changed too. Many manufacturers recommend replacing mounts whenever struts are serviced, but it’s not always done unless specifically requested.

For more on how post-repair smells develop, see our notes on musty smells that appear after strut replacement.

How to prevent or fix it

If you confirm that a failed top mount is letting in moisture, the best fix is replacing the mount with a new one that includes proper sealing. This isn’t a DIY job for most people it requires compressing the spring and realigning suspension components safely.

While you’re addressing the mechanical issue, also clean or replace the cabin air filter. A moldy filter won’t cause the initial leak, but it will hold onto moisture and make the problem worse. Learn more about how cabin filters contribute to mold smells if yours hasn’t been changed in over a year.

If you’re unsure whether suspension vibration is linked to your AC smell, our guide on diagnosing mildew caused by suspension issues walks through real-world symptoms and tests.

Next steps checklist

• Inspect the strut tower area for cracks, gaps, or water residue
• Check your cabin air filter for dampness or mold
• Ask your mechanic if top mounts were replaced during any recent strut service
• Avoid temporary fixes like ozone treatments or sprays until the source is sealed
• Schedule a proper inspection if the smell persists after filter replacement

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