AC Doctors installed a 5 ton split air conditioner and gas furnace for us. They were very professional and offered a fair price for the system we had installed. They provide a 2 year labor warranty on what they install. Most manufacturers will warranty the parts, but not the labor of this uber expensive investment and the labor can be as much or more than the parts.
As with all contractors, we researched the Arizona Registrar of Contractors, the Better Business Bureau, as well as Yelp before selecting a contractor. In selecting the model of air conditioner and furnace we researched actual consumers of these products on www.furnacecompare.com.