It's all about proper Installation !
Long time reading here (learning) mostly - question time now.
A "consistent" theme here, without regard to system manfufacturer, or even sizing to a degree is It's all about a proper installation. With literally thousands of contractors in any major large metropolitan area, they all pitch the same line.
The question is, how is one to know what is a "good install" as opposed to an "ok" or "really crappy" install? After 11 years in our house with the existing A/C (2.5 ton Carrier) during summers I've never been to get the house comfortable....the A/C ran continuously from 10 AM till 2 AM before it clicked off. And, this was for the downstairs unit! Not even discussing the upstairs yet! You can only imagine the utility bills.
So, having had 4 bids out of hundreds in my area, one actually did a computer version of the Manual J Load Calculation and it came up to minimum 3.5 ton for the downstairs (2900 sq ft / 1700 down- 1200 up)
After quickly learning the 1/2 ton units dont come in newer technology dual speed compressor / fans, went with a 4 ton Amana ASX16 seer entire sytem. Amazing now to be able to hold 68 degrees even on the hottest days 95+. System cycles high for a couple of minutes then to low speed for 15 min or so then as needed back to high speed again or off late in the day and at night.
Sorry...back to the question. Anyway...... The contractor I choose came in with the LOWEST bid, and I offered the other 3 bidders a chance to meet or beat their price - matching component to component / apples to apples comparisons- NONE of them ever called back again!!!
So.. they came out 2 days later and installed a complete new system (incl gas furnace). BBB showed in biz 22 years, 3 complaints, all resolved in last 36 months, all the certifications and members of various HVAC groups, etc, etc. - They were not some fly-by-night operation!.
As a DIY sort of guy, I feel fairly knowledged in a lot of things, especially common sense applictions. The guys did what I consider to be a nice install. Added another supply vent and a 12 x 12 return air in another location to improve circulation and add more return capacity (CFM's).
OK.. SO.. How do I actually KNOW, what is a good install and what isn't?