No floor fan while charging AC system --- effect?

[JohnHere]

Now, on to overcharge and undercharge and why they're both bad. Help correct my misunderstandings!

You have a lot of questions, you're drifting off topic, and delving into MVAC theory. Courses and webinars are available, given by MACS and others, which discuss these subjects in detail. I would suggest enrolling in one or more of those to help fill-in your knowledge gaps. Keeping it as brief as possible, some comments follow.

Obviously with undercharge, the system can't produce as many BTU's of cooling. Compressor isn't getting a nice Big Gulp of gas to compress. Too low and the compressor won't start. (Low limit switch)

Two of the main reasons that an undercharge is undesirable: 1. Causes less oil to circulate to the compressor, leading to its premature failure; 2. A low charge, while still sufficient to keep the compressor engaged, will cause the evaporator to ice-up, thus blocking airflow and result in little to no cooling.

Overcharge, the pressure rockets way up, and since it's harder for refrigerant under higher pressure to boil, change to a gas, same thing happens. The evaporator can't produce as many BTU's. AND you get greater wear and tear on the compressor, etc. Too high --- limit switch turns off the compressor. What else?

1. An overcharge overfills the system with refrigerant, resulting in little to no cooling because the refrigerant ""floods" through the evaporator without changing state—that is, it remains a liquid. 2. Liquid refrigerant might enter the compressor. Since a liquid cannot be compressed, the compressor will be damaged or destroyed. 3. An overcharge will also result in undue stress on the compressor, shortening its service life.

Obviously there's a sweet spot, in terms of charge, which everyone? almost everyone? today believes is easier to hit by charging by mfr suggested weight than by watching gauges.
How wide is that sweet spot, in your mental model? A couple of ounces? How often do you charge by weight and then decide using the gauges its still a little low or high? Ever? Never?

A lot of time and effort goes into how a manufacturer determines the optimal charge for a given system, which is also a closely guarded secret. I'm not a MVAC engineer, so I'm not privy to exactly how it's done. But in every case, the refrigerant charge is specified by weight. I've yet to see anyone who can tell me how much refrigerant a system contains by looking at pressures.

With today's smaller-capacity systems, there is no "sweet spot." The refrigerant must be weighed-in precisely for the system to operate as the designers intended.

Same question but for refrigerant oil. How many of you guys are absolutely anal about measuring recovered oil and replacing the same amount.

Best Practices state that the specified, precise amount of oil be added to a "dry" system and that the same amount be maintained when servicing a system. This has nothing to do with being "anal," but has everything to do with maintaining the manufacturer's oil specification.

TBH the guys I've hired over the years to do AC work for me - many seemed to be cutting corners, NOT doing things by the book, trying to "get done" (or perhaps limited by client budget) rather than trying to obtain the best possible AC performance.

IMHO, you won't find any consultants on this Forum who think and work that way

Which is why I'm trying to get educated so I can do it right, at least on my own vehicles.
So THANK YOU for taking the time to help me learn, and I'm sorry if I come off as a jerk.

Learning about MVAC is commendable, and there is certainly much to learn, which is beyond the educational scope of this Forum. As already mentioned, I suggest taking some courses and enrolling in webinars to get started, and coming back here to address vehicle-specific issues that you might have.