If you notice water pooling on your car’s floorboard especially near the front passenger side it might not be a clogged AC drain or a windshield seal issue. In some vehicles, particularly older models or those with strut towers close to the HVAC housing, water can sneak in through worn or damaged strut mounts and end up inside your air conditioning system. This isn’t just a minor annoyance; it creates a damp environment where mold and mildew thrive, leading to that familiar musty smell every time you turn on the AC.

How does water from strut mounts get into the AC system?

Strut mounts sit at the top of your vehicle’s suspension struts, usually under the hood near the firewall. Over time, the rubber seals in these mounts can crack, shrink, or tear especially if they’ve been exposed to heat, road salt, or age. When this happens, rainwater or car wash runoff can seep through the opening around the strut shaft and drip down into the HVAC plenum (the chamber that directs air into your cabin). Since this area houses your AC evaporator core, any moisture that enters can linger, promoting microbial growth and eventually causing odors or even corrosion.

What are the signs this is happening in my car?

You might suspect a strut mount leak if:

  • Water appears on the passenger-side floor only after rain or washing the car not during normal AC use.
  • The musty or moldy odor from your vents gets worse after wet weather.
  • You’ve already checked and cleared the AC condensate drain tube, but the problem persists.
  • There’s visible rust or staining around the strut tower area under the hood.

In many cases, people assume the issue is a clogged evaporator drain, but if that drain is clear and water still shows up inconsistently with weather conditions, the strut mount could be the real culprit. A related issue we’ve seen involves moldy smells that trace back to compromised strut seals, not just internal AC contamination.

Why do people miss this problem?

Most DIYers and even some mechanics focus first on the AC system itself the evaporator case, blower motor, or drain tube. Strut mounts aren’t typically on the checklist for interior leaks unless there’s obvious damage. But in cars where the strut tower opening aligns closely with the HVAC housing (common in certain Japanese and European models), even a small gap in the mount seal can channel water directly into the system.

Another mistake is replacing the entire strut assembly without inspecting the mount seal alone. Often, the strut itself is fine it’s just the rubber gasket or bearing plate that’s failed. Replacing only the mount saves money and labor.

How to check if your strut mounts are leaking

Start by drying out the cabin completely. Then, during dry weather, pour a small amount of water around the base of each front strut tower under the hood avoid spraying directly into electrical components. Watch inside the cabin (or use a borescope) to see if water drips near the HVAC intake or onto the floor. If it does, the mount seal is likely compromised.

Also inspect the underside of the hood near the strut towers for cracked rubber, missing grommets, or debris buildup that could trap water. Sometimes leaves or dirt hold moisture against the seal, accelerating wear. For a more detailed walkthrough of what to look for, including photos of failed mounts, see our guide on strut mount inspection procedures specific to AC-related leaks.

Can this cause long-term damage?

Yes. Persistent moisture inside the HVAC housing doesn’t just cause bad smells it can corrode the evaporator core, degrade insulation, and encourage mold growth deep within ducts that are hard to clean. In severe cases, electrical connectors for the blower motor or climate sensors may short out. And because the source is external (rainwater), standard AC treatments like ozone cleaning or antimicrobial sprays won’t fix the root issue.

If you’ve been battling recurring mustiness despite cleaning your system, it’s worth considering whether strut mount failure is letting in outside moisture that re-contaminates the system.

What to do next if you confirm a leak

Replacing the strut mount seal or the entire mount assembly is usually straightforward for someone with basic mechanical skills. You don’t always need an alignment afterward unless you disturb suspension geometry. Use OEM or high-quality aftermarket mounts with intact rubber seals cheap replacements often fail quickly.

If you’re not comfortable doing it yourself, ask your mechanic to specifically check for water intrusion paths from the strut towers during diagnosis. Mention the possibility of external water entry, not just internal condensation issues.

Quick checklist if you suspect a strut mount leak:

  1. Dry out the cabin completely.
  2. Verify the AC drain tube is clear and flowing.
  3. Inspect strut mount rubber for cracks, gaps, or missing sections.
  4. Perform a controlled water test around the strut tower (not into electronics).
  5. If water enters the cabin, replace the mount seal or full mount assembly.
  6. After repair, run the AC on fresh-air mode (not recirculate) for a few days to dry residual moisture.
Get Started