AC plenum in crawlspace sweating?
I had a brand new Trane ac and plenum installed last summer in my crawlspace, and to date it has been a nightmare dealing with a poor install. The (national) company who sold and installed the unit has already been out 7 times to "fix" issues. Last time, they took almost everything apart, put it all back together with new insulation and parts, and sealed everything with mastic "goop" and tape. The air in the house is now finally cool and dry--so it feels like they (finally) got the job right.
However, one week later I just discovered that water is puddling on the outside of the insulated sheet metal plenum and dripping off the connections to the ducts. I can't tell if it's happening on the inside too . . .
I live in the southeast, and the weather is hot and humid. However, it's only been in the upper 80's this past week. The crawlspace under the brick house is on a slope ranging from 7 to 4 feet in height and is not insulated. There are 8 vents in the brick that we open in the summer and close in the winter, and there is a sheet of plastic ~4mm thick on the floor.
We didn't seem to have this issue before with the previous AC, which was made out of duct-board.
Can anybody please tell me what is going on, how this issue can and should be fixed?