If your car’s air conditioning smells musty especially when you first turn it on it might not just be a dirty cabin filter or mildew in the evaporator case. Sometimes, that damp, stale odor sneaks in through unexpected places, like small gaps around the strut towers. These are the reinforced areas in your engine bay where the suspension struts connect to the body. Over time, worn seals or cracked grommets near these towers can let moisture and outside air seep into the cabin, creating the perfect environment for mold and mildew to grow right where your AC pulls in fresh air.

Why does the smell seem tied to the strut towers?

The HVAC system draws outside air through the cowl area the grille at the base of your windshield. Right below that, the strut towers pass through the firewall. If the rubber seals or foam gaskets around those penetrations degrade, rainwater or humid air can drip or drift into the cabin air intake path. Even a tiny gap can introduce enough moisture to encourage microbial growth inside ducts or on insulation near the blower motor. You might notice the odor worsens after rain or in humid weather, which is a strong clue the issue isn’t just internal to the AC unit itself.

How do I know if the leak is really around the strut towers?

Start by checking for visible signs. Open the hood and look where the strut mounts pass through the inner fender well. Are the rubber boots cracked or missing? Is there debris buildup or water pooling nearby? You can also run your hand along the firewall edge near the tower if it feels damp or you see staining on the insulation, that’s a red flag.

Another test: have someone spray a fine mist of water around the strut tower area while you sit inside with the AC off and windows up. If you start to smell dampness or hear dripping near the dash within a minute or two, moisture is likely entering through that zone. This method mimics real-world conditions without disassembling anything.

Common mistakes people make when troubleshooting this issue

• Assuming it’s “just” a cabin filter problem. While a dirty filter can contribute to odors, replacing it won’t fix leaks letting in external moisture.
• Sealing the wrong spot. Some try to caulk over visible gaps on the engine side but miss the actual entry point deeper in the firewall seal.
• Ignoring related components. Damaged cabin mounts or degraded cowl seals often go hand-in-hand with strut tower leaks. Fixing one without checking the others leads to recurring smells.

What to do once you confirm a leak

If you find compromised seals around the strut towers, replacement is usually more effective than patching. OEM-style rubber grommets or closed-cell foam tape can restore the barrier. Be sure to clean any existing mildew from nearby surfaces before resealing otherwise, the odor may linger even after the leak is fixed.

For a step-by-step walkthrough of inspecting these seals yourself, including what tools to use and how to access tight spots, check out our guide on doing a DIY inspection of strut mount seals. It covers common vehicle-specific quirks and shows exactly where to look on popular models.

Can other parts cause similar symptoms?

Yes. Worn cabin air intake mounts or torn cowl panel seals can mimic strut tower leaks because they’re all part of the same airflow path. If your strut tower seals look intact but the musty smell persists, take a closer look at the cabin air plenum area. We’ve seen cases where damaged cabin mounts allowed just enough flex to create micro-gaps that pulled in humid air during driving.

Also, don’t overlook the AC drain tube. A clogged evaporator drain can cause standing water inside the case, which produces a similar musty smell but that odor usually stays constant, not worsening after rain or car washes like a strut tower leak would.

Next steps to stop the smell for good

1. Dry out the HVAC system by running the fan on high (without AC) for 10–15 minutes after each drive.
2. Inspect the strut tower seals and surrounding firewall gaskets for cracks, gaps, or compression loss.
3. If leaks are found, replace seals and clean any affected insulation or ductwork.
4. Check related entry points like the cowl panel and cabin mounts this overview explains how they interact.
5. Consider using an HVAC deodorizer designed for automotive systems, but only after fixing the source of moisture.

Fixing the root cause not just masking the smell is what keeps your cabin air fresh long-term. Most strut tower seal issues are straightforward to address if caught early, and doing so prevents more costly mold remediation down the road.