Originally Posted by Sierra360PDEK
My A/C ducts are made from what appears as cheap ductboard. Only Styrofoam I've seen is inside the A/C separating the intake and out take air supplies and in my sidewalls. The A/ C duct does run almost all the way to the front wall though. Still cannot see how water would run down the ductwork and into the nose cone as the duct does not penetrate through the front wall into the cap.
There is a layer of Styrofoam that the duct channels are bored through. (at least in my unit) it runs from the front to the back the whole unit is about 4 or 5" thick water will not penetrate Styrofoam. I do not have any batt insulation. There is a then layer of silver bubble insulation that lays on top under the roof sheathing. So you have rubber roof wood sheathing silver insulation then the Styrofoam and last your ceiling board. It would not have to drip on your ceiling. If the OP has done what he has said already It COULD be running between the sheathing on top of the styrofoam. Things that have been sealed.
1) ester bound and lap sealed the top edge.
2) removed and resealed all the penetrations in the area, maker lights and scare lights
The water has to be coming in from above that area on the roof. I think we are all guessing giving him ideas. It must be a frustrating thing to deal with. I think the best way is to remove the pan take a hose to every area and look up and see where or what spot it's coming in at. Or dry it out do one area at a time and check before you move on that it is still dry. I sill get styrofoam blowing out of my registers and dropping into my ceiling lights after 4 years of use. Just as Bob Caldwell mentioned. I know nothing of cheap ductboard ducting, but your unit could be different....