1999 3/4T 4x4 w/Cummins.

Water is mysteriously collecting under the mat on the passenger side of the truck. A LOT of water. Drenching the whole floor. I know it isn't coolant or from washing the truck. I guess it is water from the a/c, but where is it coming from? I see no signs of any dripping...
Anyone else have this problem?

 

I had this problem. For me it was the AC drain. What happens is that the foam seal breaks down over time. Water seeps out slowly and rather than drop it runs on the bottom of the drain back to the firewall. It then seeps into the cab. I had to lift my carpet for over a week to let it air dry.

The problem is that the drain runs horizontal and has no drop to it. The solution is a hose with a little droop to it. Now the water flows out and cannot flow back to the firewall. I used a 5/8" x 6" piece of garden hose. It was tight so I did not have to use a hose clamp. Been dry ever since.

I did the same fix on a Jeep. The big trouble there is that the drain is sealed inside a frame rail. I had to first find it, then I cut a hole in the steel rail, put the hose on, and screwed on a cover plate to hide the hole. That vehicle has been dry too.

 

From the second gen section...

https://dodgeforum.com/forum/2nd-gen...loorboard.html

Could be a lot of things including 3rd brake light seal, ac drain, door/window seals. Have someone hose the truck down with you sitting inside looking for leaks. Good luck.

 

Yeah, I have owned 3 of the 2nd gen Rams and they have all had this problem, first time I experienced it was on my 1997 3/4 Ton, for quite a while all the windows were fogging up and the cab was starting to get a bit of a smell when you first opened the door, so after alot of trial and error, I was left with no answers so.... only one thing left to do I gutted my Interior, No seats, no carpet, no plastic moulding around the doors and I got my Neighbour to run the hose overtop of my cab while I was inside and within about 20 seconds a slow stream of water started dripping in, on further inspection up under the dash showed it was leaking from the firewall, all I did was silicone it and the problem never arose again, did the same thing on my Cummins when I bought it except I gutted the entire interior and sealed the floor with silicone everywhere water could somehow get in and then coated the entire floor from wall to wall with rustoleum rust paint, put er all back together and havn't had a problem

another area where water commonly seeps in is beneath the step guard, theres about 6 holes where the screws go in, they go right through the bottom of the cab and poke out, just look for little areas like that and seal them up good.


Hope that helps you

Good Luck.

 

The AC drain goes out on the passenger side. Pull the top of the carpeting out and you will see it. Place a paper towel around the drain box and run your AC. If the towel gets wet, that is where it is entering. It just seeps in slowly. I did the towel test and had it get wet each time.

If the towel does not get wet, this would eliminate the AC drain.

With the humidity being lower now, you may have to run the AC longer to get water out.

 

Update on this. I attached a 5/8" x 1' hose to the a/c drain, dried out my carpet, and over a week later now no wet carpet. Think $1 worth of hose from Lowe's did the trick!
Thanks for all the suggestions, guys!