2004 Altima 4cyl. This is weird. I cannot locate the AC's drip tube that allows excess condensate to drain out under the car. I have the Haynes manual which shows roughly where it should be, but it isn't there. And, get this, it appears to be dripping behind the floor mat inside the car and has rusted out the floorboard on the passenger side (which I had replaced). The auto body guy couldn't find the tube either. This should be an easy fix (clogged tube = push something through it to open it up) but the exit opening for the tube can't be located. Anyone come across this?

Let's look at the FSM - here ya go: www.nissanservicemanual.com

AZ, thanks for the link to the manual, now that's some detail! I found the AC section (only 130+ pages) but could not find any mention of the drip tube. Not necessarily surprising since it's a minor, non-mechanical player. So, I rolled up my sleeves and decided to tackle it myself from inside the cabin. Within several minutes I uncovered the drip tube; duh. I had been looking for it from the outside and just didn't get intimate enough with it. I pulled the tube off the bottom of the heater box and blew through it, clear; then I connected another tube up to the tube outlet and blew into the heater box, clear going backwards. I then laid a tray under the other end of this temporary tube and started the car, running the AC at full tilt. The condensate dripped out into the tray as it should. Conclusion: the drip tube operates properly without any leakage to the interior of the car, there's also the appropriate puddle underneath on the driveway. So, what now? Am I right to now suspect the interior leakage to underneath the floor mat may be coming from a poor seal to the windshield? Or...?

Nice work, Sherlock!

I think I'd pull the carpet back, roll up the windows, and take the hose to the car. Someone sitting inside with a strong flashlight should be able to spot the glint of water intruding. I wonder if maybe it's coming in from the cowl... weird!

I may not be able to get to this until the next weekend. In the meantime, what do you mean by coming in through the cowl?