A/C not blowing cold and hissing sound coming from the center vent when turned on

Okay, A/C on my wife's van stopped working about a month ago.
It had a hissing sound coming from the center vent when turned on. I checked the low side and it was around 20 lbs. So I went and put a can in it and when I disconnected I could hear a small hissing sound. After checking found that the valve was leaking. After taking it out found it was bent so I replaced it. Was good for a few days but I noticed even when working it wasn't cold like it should have been. It was cool, but not quite right. After a few days it stopped cooling again. Blowing just fine, but not cool. I checked it again and it had dropped down about 5 lbs. Rechecked valve and seemed okay. Put more 134 in it, got it to about 45 lbs and let it go. After about 4 days (today) it has stopped blowing cold again.
More information: I have dye tested it. Could not find anything. Compressor kicking on, voltage is fine. Condenser not leaking. Here's the kicker: about 6 months ago the car was leaking into the passenger floor. Learned that this car has a design flaw where the evap core has a small drain that hardly sticks out of the firewall, so I had put an extension hose on it and it seemed to work fine. Now about a week ago she said her floor board was soaked again. Now I'm wondering if the problem all along was a leak in the evaporator. How can I test this? Not really wanting to pull the darn dash out if I can help it. Could it be clogged? Would that cause lack of A/C, or the hissing? I'm guessing leak in evap but hoping not. Thanks for reading this book. Lol.