I've had 5 years of automotive experience and thought I had a basic understanding of heating and A/C fundamentals and I was correct in the aspect of it being basic. Living in upstate NY a/c problems generally only come in half the year and it's typically a inject dye and replace line or replace obvious faulty part. Many other well informed tech I know have mentioned that this was one of their struggles for ASEs and I think the reason may be which I just explained, diagnosis around here is relatively simple and quick. Besides all that I certainly could not have passed without this book, as long as you absorb all the explanations it will help you immensely, first times I took the practice tests I did horrible, after a few retries and studying for about 2 weeks I ended up taking my ASE and passed with a 40/50. Like mentioned before I know several techs that are far more experienced than myself and they all told me that A7 took them several times to pass. Only reason I'm giving a 4/5 is compared to the other Delmar-Cengage books I've used, this one seemed to have the most amount of typos and poor editing points.