Why are there different torque values and tightening methods for mini split flare fittings? Is there a generic procedure?

[gagecalman]

Why are there different torque values and tightening methods for mini split flare fittings?
Is there a generic procedure that can be used?
I looked at several brands and some recommend tightening to a specific torque value and that's it.
Some recommend tightening to a value, then loosing, then tighten to the same value or something a little higher.
All of the torque values are different.
Some wrenches that are made for this purpose have a chart that show different values as well.
So I was just wondering why. Is it that they use different fittings, nuts or copper? Maybe different wall thickness?
Well thanks for reading!

 

[fitter30]

All refrigeration tubing is L copper that is clean, dry and sealed. What ever size there will be a certain thickness can look up the specs. Before minis never new the was a spec. Never seen a torque wrench for flares and must of made a few thousand flares over 45 years working. But with refrigerants i was using them on 350 - 400 lbs of pressure was the max. 410A came out everything i saw was sil- fos because of the higher pressures. There are different styles of flare nuts with 45° angle. Manufacturers want you to use the ones that come with the units not the ones on the line set.
Engineers that write these install manuals have to justify their position and with their factory supplied flare nuts I'm going to use their recommendation. Their are industry standards and industry practices. Standard go by the manual, practice you know more than the guy writing the manual.