Water coming from underneath passenger dash board onto rug.

I have the same problem on the same vehicle. It is definitely A/C condensation. I cannot find any plugged drains. If I run the Rainier with the passenger side carpet pulled back, I can see the leak begin a few minutes after the A/C is turned on. It makes about 1 gallon of water an hour. update; This turned out to be the A/C drain tube located on a nipple sticking out from the firewall, next to the A/C hoses. Pull the tube, be prepared to get a lot of water, then clear the tube and put it back on.

Thank you much. That's exactly what I found. The drain plug was clogged with alot of old leaves.

Thank You, Thank You...Thank You!! Exactly what it was...Mechanic would have charged me 300 bucks and told me "your water pump is backed up" and I would have believed it and paid it. After all water coming into the cabin looks like a serious problem, and the water pump has to do with water right?? Pulled the rubber hose, water came out, cleaned it with a rag and plugged it back in...30 seconds and the problem was solved.