While used portable air conditioners are easy to find online, most used central units are purchased through an installer or with a local store acting as a middleman. Most homeowners keep their existing air conditioners for as long as possible, which means used systems are often prohibitively expensive to maintain.
While used air conditioners cost less than new air conditioners, much the cost involved with installing an air conditioner deals with the labor involved. In addition, especially old units might be unfamiliar to installers or require special parts no longer manufactured, which can drive up costs. This, combined with the superior efficiency of newer air conditioners, leads most people to opt for new central air conditioners.