I understand the importance of using nitrogen when brazing to eliminate that black build-up of "soot" on the inside of the joints. I personally did an experiment brazing with and without nitrogen and then cut open the copper to see for myself. No "soot" with nitrogen!!
I do have questions about blowing nitrogen thru the line-set after a repair to help remove moisture before pulling a vacuum. I've even read flushing nitrogen several times while pulling vacuum is the best way.
After finishing a repair I always add 250 lbs of nitrogen and watch my gauges for about 10 minutes to make sure the pressure does not change. I assume this verifies the system has no leaks. When I vent the nitrogen is this considered flushing the system or do I need to blow nitrogen actually thru from one service valve to the other to do it correctly? To flow nitrogen thru the line-set to the evap coil I close off one of the sevice valves to force it thru but how do I force the nitrogen thru the condensing unit if that can even be done?
I work on residential or small (up to 8-10 ton) commercial units.
Also I hear allot about not using gauges to vacuum a system because they are "charging gauges" not "vacuum gauges". How critical is this?
Any help on this would be great.