We installed a new forced-air furnace and A/C system in our house 6 years
ago. The A/C system is Puron and until very late last summer the system
worked great; on the last cooling day of the year (more humid than hot), the
expansion coils iced up and the system would not cool.

We had it recharged right before memorial day and I asked the service guy if
loss of refrigerent was normal -- he said no, it's supposed to be a sealed
system but tiny leaks seem to happen and that I shouldn't worry too much
about it -- every 5-6 years needing a recharge isn't bad considering the
service life is probably around 20 years.

The system worked well until the past couple of weeks when it seems to have
trouble keeping up with very hot days (90F) and two days ago when it iced
up again, which leads me to believe the 5-6 year leak has become a 2 month
leak I need to have more permanently fixed.

What's the industry best practice for solving these leaks? Is the supply
line itself a culprit or is it typically just the solder joints at the
expansion coil or the coil itself? Is it a soap-and-water mission over all
the joints, or is there some high-tech tool to check for pressure losses?

What I'd like to avoid is a knee-jerk fix (like ripping apart sheet metal to
replace the coil when it doesn't need it).

The thing I'm most worried about is a leak in the line itself, since most of
it is soffited in an area of the basement that's been remodeled (a year
after the install, so likely not a source of a puncture).