Regarding the fittings, you'd need to find from the maker of the fittings what pressure they're rated to fail at.
May I ask why you suspect the lineset beneath the slab has failed? Copper pipes in slabs can sometimes fail due to being in contact with iron rebar (electrolysis) but otherwise are typically pretty stout under there. Do you think the possible failure is related to the high pressures the solar assisted system operates under?
Regarding your energy savings, did I read correctly you replaced a 13 SEER Goodman 2.5 ton unit? And if so, what SEER did you go with as a replacement, and was the tonnage the same?