Perhaps it's metric.

Air conditioning for autos is completely different animal from a home air conditioner. Different service connectors and different refrigerants, completely different application.

Youtube isn't necessarily a good place to get an edumacation, there's more misinformation there than anything that is going to help you do this yourself. So many things to consider: The person making the video may not have an education, they may have stumbled into the occupation from a maintenance profession, learned improperly from someone who taught them and so on.

Or you're mixing skill sets. Like those who work on cars (mobile refrigeration units) versus those that work on refrigeration versus those that work on residential AC units. While these systems do the same thing, there are differences from one application to the next. This is where a 'GOOD' education comes in.

This is why people who want to really do this go to trade school and spend $20k - $30K for a real education. (This type of education may cost more now. 2019)

In fact, you really have to be careful of the information you get here as well.