need help for brazing HVAC lines

[hammerdean]

What is the best roll of silver brazing or rods that will flow using mapp gas?

[monkey spanners]

For copper to copper i'd use 5%, for copper plated steel, txv's and service valves 15% and for dissimilar metals like brass and steel you'll need a rod with a silver content about 40% and a suitable flux. Make sure your torch has a high enough capacity to cope with the line size you are working on, prolonged heating will cause poor brazed joints, i think the silver boils off when heated too long making porous joints.