We've been remodeling our house for the last couple of years and I think I jumped the gun a little bit when I bought a new HVAC system 3 years ago. Never installed it, but now I'm getting ready to. It's a Goodman (96%) heat and air. My question is does the refrigerant (R-410a) 'go bad' from sitting? It's a 'pre-charged' unit from the mfg. Is there anything else I should be concerned about by it sitting for so long? My HVAC guy (my son, but he's young - 25) said it shouldn't be a problem, but it's winter time and I want to get it right the first time so I don't freeze my arse off because I screwed up.