[cabmandone]

On the refrigerant lines, some come pre charged so installers can't cut and braze fittings like they would using copper that just has a nitrogen holding charge. Many won't braze because to do it properly you need to flow nitrogen to keep impurities from forming while brazing. Does it look bad? Yep... does it hurt function? Nope. I was a painfully picky installer because I knew that something looking off leads a homeowner to look for more.

My guess on the duct is that he didn't want to end up going below the metal pipe because that would put the vent pipe below the main trunk and that would mess things up for framing a bulkhead and boxing the duct in for a drop ceiling.