Air conditioning units with a SEER rating of 11 to 14 tend to hold up best, according to the study. A system with a SEER of more than 14 tends to be more complex, with more that can go wrong. Another thing to consider when replacing a unit or installing a new one is matching new equipment with old. Compressor type also is a factor. Scroll types are pricier, but they tend to be higher in efficiency and quieter than reciprocating compressors.
Most manufacturers offer both types.
Older or larger multistory houses often are divided into several heating and cooling zones that require a damper-zoned cooling unit. This type of system is complex and may require more repairs. Any central cooling system can have trouble, so it's important to maintain it after making sure that it's a reliable brand and properly installed.