A musty smell in your car can be from a few different things.
You may have water entering the vehicle from any number of places and it has gotten under the carpet. A leaking door seal, windshield, plugged sunroof drains,, etc.
Or this can be a problem with the A/C evaporator drain is plugged and casuing a mildew build-up in the HVAC case. Water testing for a leak can be a very difficult task, since water can leak into the vehicle from a spot that is nowhere near the final resting point of the water.
TechJK
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