Trying to trace down an evaporator leak that all of sudden developed, I know it was draining totally fine until recently it started seriously dumping condensation into the carpet. I pulled the carpet away from the blower motor / passenger foot rest area, turned the ac on and tried watching for water coming from below the plastic housing surrounding the evaporator and blower motor. It soaked the carpet within a few minutes of the ac being on, but I couldn't see where it was coming from! The vent hole in the engine bay, below the filter/dryer seems to be open. With the blower on you can feel air coming out of it. Going to do a further carpet rip out and try this experiment again.

You might try blowing some compressed air into the drain outlet or you may have just built up a bunch or crud inside the evaporator and plugged the drain channel. Remove the fan resistor pack and look inside.

Isn't there supposed to be a little rubber hose from the evap. housing to the hole in the firewall? If there is, it sounds like yours is missing.
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1955 Human, Scott; 1991 745 Turbo, Brunhilde; 1990 745GL, Snuggle Bunny

My 740 was continuously leaking and soaking the carpet on the passenger side. I checked and the drain hole thru the firewall going out to the engine compartment was completely clear. After pulling the carpet and mat out to dry, I turned on the AC to find the leak.

Turns out it was leaking as a constant drip right where the pan met the firewall. There is a foam gasket there and it was running right down the firewall into the floorboard. I tried silicones at first, and it still leaked. However I did find something that finally sealed it up.

I got a bottle of Gorilla Glue. I then stuck it up under that foam rubber seal and squirted a bead all around that thing. Left the thing to dry for a few hours and it expanded and sealed it up. Has not leaked a drop in 5 years.

I have also used that Gorilla Glue to seal up my threads on the chicken waterer bottom of the bucket where the valve attaches. 6 years out in the weather and that thing doesn't leak a drop still.

Again, in my 240, wet floorboards meant stopped up drain hose and it could be that in yours. If the drain is working properly, then maybe you have the same problem I had.

good luck!

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93' 240 Classic Wagon 220K & 92' 740 Wagon Regina/Rex 90K