The sales experts tell us that on average a person will buy one central air conditioning system in a lifetime. That doesn't leave much time to gain experience so you tend to rely more on advertising slogans and flashy visual hype than with other household appliances. Consumer testing publications are not much help. The installing contractor has so much influence on how well the product works that can not be duplicated in the laboratory that testing is only done on small appliance type air conditioners. Some information is available on how a well installed system performs and whether the installations were reliable but that does not guarantee you will get a contractor who will do as good a job. Your friends and neighbors are some of the best sources for information on reliable and unreliable contractors.