As I said before I have experience in both residential,& commercial refrigeration air conditioning and energy management this book gives you direction where to look first what to look for what each component looks like and its function gives a couple different scenarios what could be wrong and how to fix them and if after doing some of these diagnostics it may help you decide if you should tackle the job or wait for a professional but if the problem turns out to be a component that cost less than a 40 bucks you'd be saving a lot of money given todays service companies charge upward of a hundred dollars and hour plus parts