I have a York 3ton ACthat is starting it's 13th summer. The coil is what I believe you whould call a slab type (not a a-coil) I have a problem in that it drips all over this inside the furnace (upflow).The water does not channel down between the fins to the drain channels. It started a couple years ago and I suspected that it could be dirt buildup. I secured the coil to the plenum and the plenum to the ceiling so that I could remove the furnace out of the way and get to the coil for cleaning.(Why do contractors install coils directly on top of the furnace so there is no way to even look let alone clean the coils?) It was dirty so I brushed the heavy junk off with a brush and purchsed a commercial grade foaming cleaner to wash and rinse the coil. Replaced furnace and ran unit. It helped but did not totally eliminate the dripping. This is the third summer and I have cleaned it again but still dripping.I have just installed a new furnace that is shorter. I extended the plenum down to the furnace temporaily with clear Lexan so they I can directly veiw inside while the unit is runnig. Other than this problem the unit cools and dehumidify the house well.