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Last week I was changing out a compressor in a Hydron Module water to air heat pump. This unit is a 2005 vintage unit and the factory brazing in the unit did not look very good. So when brazing in the suction line to the compressor I could not for the life of me get this to seal up. Pipe and compressor fitting were perfectly clean, no oil or residue. I tried for a few hours and gave up. I'm using Sil Fos 15 so copper to copper joints are good to go with no topical flux.
The next day I tried again and put a very small amount of brazing flux on the joint on my next try, sealed perfectly.
I typically do not use any brazing flux but now I'm thinking about using it on second hand joints such as this one. Also when making connections to brass service valves. I know we want to keep the interior piping spotless but a very small amount really could make life easier.
Anyone use flux on a regular basis with copper to brass or second hand joints in a refer system? I'm guessing its not all that popular with how hard it was to find. 1 supplier had it in stock and the container was 5 years old.