Reading. A/C stuff comes from my neighbor, Specialty Air, I would say about 95% of the trucks in western Pa. He and/or his shop have been through every one. A lot of the mining equipment in the area is serviced by his shop. Cars and RVs when not under warranty. He does not do manufacturer warranty work, too cheap. I have spent a lot of time over there and a bit of money. He loves trucks and farm equipment so if you want to BS with him a while just talk about those. He has helped me tremendously with truck stuff and attitude on dealing with repairs. One of his best lessons was if something is breaking keep heading for home. Shorter tow bill, and the parts are ruined anyway. If you make it use the money saved in the tow to start buying parts.
Reading and attention to detail is everything else. You also have to not dreamer the problem. It is a machine they all work the same. Stop dreaming up ways that your problem is different from all the others. It's most likely the simplest thing. Like how many times have we had new people on hear that have complexed their problem into a mountain, and then Big John fixes it in one sentence.
It's not rocket science, and even that is not difficult. Landing now that's a problem.
Back to A/C. Did you know the real reason for R12s end?
Charles Kettering VP at GM assembled a team to develop a refrigerant (cheap) the team brought in Dupont to help develop what became known as R12 while the original GM team had their names on the patent, once automobile A/C started to become more normal it was tweaked and Dupont ended up with it. So no matter what brand was on the bottle Dupont was getting a cut. When that patent was expiring in the 90s Dupont was on the edge of "Freon is bad for Ozone" and just so happened to have the patent on the most viable replacement R134a. Now we all know that 134 is now bad for environment as patent is running out and, wait for it...... Dupont holds the patent for R1234, and on top of that they made it non convertible meaning you cannot convert your R1234 system back to cheap 134a and you cannot convert your R12 or R134 to the sometime only one available R1234. Bravo to Dupont for making a product that gives way to the successor all while holding that patent close to the vest. I'm sure a retrofit will become available, but you can bet Dupont will have their hand out. Well played!
