Scene of the crime, 1981 block home, 1500 sq ft under air, Air con system was probably as old as the house, circa 1981.
Summer of "05 one main duct started sweating and stained the ceiling. The other main duct going to the other side of the house stayed dry.
This was the first time in our four years in the house this had happened. I at first thought it was because we had a large get together the week before and the system ran for several hours straight.
So last winter I patched the ceiling (btw I hate popcorn ceilings), and replaced the insulation in that part of the attic (I'm not so fond of fiberglass batts either)
This summer it happened again so I'm trying to figure out why after 24 years the ducts started sweating ? Then the light bulb went on. I had closed three out of six ducts on that side of the house to force more cold air into the master bedroom (The Mrs likes it REALLY cold when she's sleeping).
I suspect that closing the vents caused that duct to chill down so much it started sweating. Is this a possible scenario or do I need to look into other causes ?
Thanks for your time,