Pontiac: wet floorboards, drain tube, drain hole

Question
What would cause my floors in my 1996 Transport SE to flood. It happens when the AC is running.

Answer
Oooh, this is any easy thing.  The evaporator, which is the device that cools the air in the car, usually makes a lot of condensation, and drains out a drain tube in the heater/AC box.  It could be two things.  Usually the box is sealed in some way at the bottom, so that if any spillage occurs inside the box water won't spill into the floorboards.  Or it could be that there was no sealing element which is usually the case, and the little tube somehow got clogged.  The tube being the one connected to the drain in the box under the evaportor.  I have a similar problem on my Fiero, only it doesn't drain very well if standing still, but the minute I start moving all the water pours out underneat the car the way it should, and if I sit with the A/C on for a long time, it will start dripping from the seam of the box(it's usually two or more pieces.

If you are mechanically inclined you could go in there and take off the part of the heater box, from there you can usually access the heater, and the Evaporator which is close to the heater.  You might be able to see the drain pan in there and maybe a drain hole.  If you can get a hold of compressed air I would blow out that little tube and see what happens.  If that fixes your problem, then it was probably clogged, if it does not you could try sealing the part of the heater box that is leaking by removing it and sealing it with silicone when you put it back together,  I did that and haven't had any problems.  Although, if your car is leaking a lot this might not be a good idea.  Most likely this problem is a clog in the drain tube, from under the car sometimes you may be able to find the little tube, maybe that will show something that might cause a clogged condition.
Hope this helps.