My 99 GT cannot be left in the rain, or it develops a serious swamp on the passenger side floor. I've read in the FAQ about a similar water leak in 97 and 98 GP's and associated blowing of the rear speaker due to water dripping on the amp, but my sound system continues to be fine. When driving in the rain, if I turn left, I will hear a sound of water hitting the fan, so I am guessing this problem has something to do with blocked drains from the cowl area causing an overflow into the interior air intake. I have checked the drain from the AC evaporator core, and it is clear. (it's not AC season here in Canada anymore anyways...)
Anybody heard of this problem?
Thanks

Do you have a moonroof?

When I had the same problem, it turned out that the water drain that drains from the moonroof track / channel had gotten clogged up and instead of dumping water somewhere behind the wheel, it leaked it into the car.

It was under warranty at the time so I had them fix it.

It happens in other cars as well, as I remember having to take my mom's Acura Legend into the dealer for the same thing once. Good luck!

I, along with countless other GP owners, have experienced this problem first hand. In most cases it is due to the AC Drain Plug being clogged and thus water overflows into the passenger floorboard. The AC Drain Plug in underneath the passenger side black cowl (accessible by going under the hood) and simply unclogging it.

Hey stick,

I just had this problem w/ my GTP. After summer had gone away, and the AC was no longer being used.
When you use your defroster, the AC automatically kicks on and off, therefore, creating the condensation that needs to be disipated. I see that you said you already checked that, but, if it's not the sunroof causing the problem, I would do a double check on the condensation drain. Mske sure you are checking the proper outlet, and that it is not blocked back in the housing itself.....Sick a wire or something that will take the bend into the housing.
Later now,

Thanks for the replies. I don't have a sunroof or moonroof. I also rechecked the AC drain and it is still clear. It is definitely related to rain, as the first time it happened I had left the car outside overnight and we had a flash-flood kind of rain. When I got in the car the next day, the pass side was sooo full of water it actually overflowed from the front floor into the back! Literally about two inches of standing water inside the car. Checked all the windows - all up tight. The second time it was caught in the rain, the same thing happened.

While it was still raining, I pulled the lower trim from under the dash and I saw water dripping from between the AC box and the firewall. As soon as I get a chance on a dry day, I'm going to run the hose on the windshield, let the water drip into the cowl vents and see if any comes in. I'll keep you posted.

Man, If there's water in the fan housing...the drain is not working properly, unless.....the housing is not part of the same assembly that utilizes the drain. This is not the case IIRC. I'd really like to see what you find to be the problem here.
One more thing.....The only other place I could think of the water coming from is the windshield seal. If you've had the glass replaced recently, goto the place that did it, and tell them U think it may be leaking. Either way, I still feel the drain is not functioning, since you can hear the fan sloshing water. Man, I love troubleshooting......NOT!
Later now,

I tried the garden hose on various parts on the car trying to reproduce the leak. It appeared to leak badly when the water was sprayed on the lower right corner of the windshield. Thinking it was the windshield seal, I took it to a reputable glass shop. Dude looked in over and declared that the seal was not to blame (it is the factory winshield and had never leaked before now - plus he claims he could see the water marks coming from the evap housing. He figures it is the gasket sealing the AC evap unit to the cowling/firewall at the fresh air intake. I went to GM parts dept. and told them the story. For the gasket kit, it is $140.00, so I want to be sure this is in fact the problem before investing in parts and labor. Has anyone ever removed the evap unit from their GP's? I don't understand why this would suddenly start leaking from this gasket. Personally, I'm still more suspicious of the windsheild than anywhere else, and will get another glass shop opinion later in the week.
Thanks
Stick