You sound like you've had some experience. That's a lot of refrigerant in the system, I'm sure they would not like to have it all leak out.
As to wet rag the fittings. The flux needs to be removed, or it will keep corroding the metal away. Yes, it makes it pretty, but it also has a very important reason. So the fitting doesn't corrode out in a couple years.
You sure you didn't come over on the boat with Lehi and Sariah in 600 BC?
Christopher A. Young Learn more about Jesus
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Long before silver solder or sil-floss was on the market, we used 95/5 solder on refrigeration joints. This worked just fine for R-12 as well as R-22 units. Granted, silver solder/Sil-floss is much better but a good weld with 95/5 worked well then and will still work today. I don't think I'd use it on the new 410A systems.
Our organization bought into 3 of the 9 R-22 machines that were built with Catepillar V-8 Engines driving the open drive compressors. They were built by a company by the name of EnChill and after 9 machines ran out of the country to Europe where they use Rolls-Royce engines instead of Catepillar. Soft solder was used on many connections and of course, the vibration of the engine opened leaks on a regular basis. The vibration of the machine caused issues with the engine controls as well.
This 450T machine held over 800 lbs of R-22 so any leak was considered catastrophic. I finally tired of fixing soft solder and used sil-floss on all of the copper connections, replacing most of it with
304SS flare fittings. Never had any leaks on the three odd machines though one of the more problematic of the three was replaced with a Trane Ice Bank machine, a great choice.
All things considered, sil-floss/silver solder was the best choice for a weld. There is a paste (I think it was called Force) that I used even though sil-floss doesn't require paste and I liberally pasted the pipe and fittings. Using a wet rag as soon as the weld was make, I wiped off the pipe which left a nice golden colored weld without the black staining you get from Sil-Floss. It gave the job a term we used to call, "Shining the job" which contractors didn't want to see you spending time making the work "look nice".
Before I sound older than the Widow's Son of the tribe of Naphalai, I'd better quit here.
John