my experience with AC units is that if they are installed properly, and cared for, other than a cap going out of tolerance, they last a very long time. I think the last AC unit we put in cost me about $2000 over a 20 year period excluding upgrades that were non-refrigerant related. If I were to work on mine I would want a complete Fieldpiece setup with manifold and all the blue tooth devices. Pressure sensors, temperature clamps, one would need a charging scale and some brand of quality vacuum pump. A good brazing set, FPM measuring meter, manometer, combustion analyzer, maybe hold off on a leak detector unless one had a leak. Accurate capacitor meter. A recovery tank, plus the small nuisance items to install Schrader valves etc..
On the other hand, I can get the PDF for my unit for free, study the specs for free, measure the distance with a tape measure every DIY has, determine the proper gauge supply wires, copper lines, breakers, etc., make sure the people doing the work aren't cutting corners there. Ask any tech when the last time was they calibrated their equipment and their eyes will cross. A temperature probe can be calibrated in a boiling pot of water if you know your elevation, and you can let them use the pot you have in your kitchen. The last guy who did that assured me his probes were accurate - they ended up being about 10F off. That changes subcooling and superheat quite a bit. You can check the tesp pretty easily if you have a manometer, and set your system up for perfect efficiency. A Klein manometer is about $120 or a UEi about $170. The UEi kit is $250 on Amazon. I think I they were about $170 when I got mine. There is a lot someone can do without the 608 and without any investment. Then just hire someone to recover and charge the system if it is ever needed. Have them come out once a year to check subcooling and superheat. It is the equipment to do it right that makes it too expensive for a DIY situation. Now if someone has a big family and helps out their friends, kids, and siblings etc., it probably pencils out other then when something else breaks make sure they don't blame you. You find the system is low on refrigerant - fix that and six weeks later the compressor goes out. You won't want them blaming Uncle Bill. Someone doing it for a living is factoring in those type events into their prices.
From a standpoint of gaining knowledge - I'd say do it. You can't lose there. But if the idea is to save money, it might not work. And many wholesale HVAC dealers won't just take a 608 to sell to. Most out here want a contractors' license before they will sell to you. Occasionally some will work with you if you can get their front office to set up an account for you and you hold EPA cert(s).
