Hello, I recently moved into a new home. After cutting into the drywall in the garage for another project, I found some mold on the face of the fiberglass insulation and proceeded to tear out a section of drywall and insulation. I found a ton of condensation running down the a/c duct (metal oval pipe). The wall section is 2x6 stud consisting of drywall on both sides, with R13 paper backed fiberglass insulation between the studs. The duct is behind the insulation between the insulation paper and interior drywall of the family room. This leaves about 3 inches air gap between the insulation and the drywall on either side of the duct. I contacted my builder since the house is under warranty and he sent out his HVAC guy. The guy said he didn't know why there would be that much condensation on the inside of the insulation, but said he would wrap the duct in foil backed insulation if my builder would do the drywall work and put back the R13. I previously had a major mold problem in another home that made our family ill so I am paranoid of mold and concerned that this fix won't be good enough long term. I've been advised that hvac ducts should not be on the outside wall like this but I'm not sure if that's true; also someone suggested I remove the drywall and fill all the spaces in the wall cavity with closed cell spray foam. This seems like a good fix but is very costly, and the builder might not go for that so it could be on my dime. Btw, I see from the basement that there are a total of 4 ducts in this wall (I have not removed drywall from other areas to see if the moisture problem is consistent). Any thoughts on the cause of the condensation and good solutions?