Air Conditioning - A/C condensation drain line sweating PROFUSELY!

Had new 2-speed, 16 SEER central A/C units installed in the attic above the second floor. This new unit seems to do a great job removing humidity from the air. But this ice-cold water, while flowing through the PVC drain line into a plumbing vent pipe, some 15 feet away, causes LOTS of condensation on the underside of the PVC drain pipe. This condensation runs down the pipe until it reaches a 90 degree turn, drips off onto a 2x4 header plate on top of a second floor wall, disappears into the wall and finally reappears dripping through a light fixture on the first floor into a bathtub (yeah, THAT part is lucky). I bought the expensive foam rubber pipe insulation, covered the PVC drain line from stem to stern, sealed all joints with duct tape, and there is STILL CONDENSATION dripping off and making the trip to the ground floor bathtub. Now what? Encapsulate the 3/4 drain pipe inside a 2 inch PVC pipe and warp the whole bloody mess with 12 inch fierglass insulation batts?

The pipe is still geting air to it! If you put rubatex on it and it is sealed then it will not sweat. Try and re glue where you see the water.

Now, after super-insulating on the PVC drain pipe, I suspect that perhaps there is condensation building up on the 2 inch vent pipe traveling down into the house - but have no way to verify except to tear into sheetrock. This is starting to suck.....I still have 6 drops per minute leaking into the ground floor, thru a light fixture, when the A/C is running

Now, after super-insulating on the PVC drain pipe, I suspect that perhaps there is condensation building up on the 2 inch vent pipe traveling down into the house -

I have no idea what a 2in vent pipe is! Why would a vent pipe go into the home? Mybe you have a install problem.

I think you have a leak and/or a blockage of the condensate line. In my experience, PVC rarely sweats and if it does, not in the quantities you speak of.