I’ve lost count the amount of times the HVAC on my vehicle has been looked at. Sometimes days at a time, but yet no permanent fix for this issue has been implemented. The HVAC has not been replaced (yet).
The attached photo is from a couple weeks back, after about 4.5 hours driving. Only when the humidity is high (Sydney) does this occur. No external water is on the ground of my parked vehicle, ever. The water under the floor mat is much more than what you see above in the photo. Funtimes
edit: yes I have carpet. It’s been fine, but acts like a sponge