We just had a new American Standard air handler with a 15KW heat strip package and the matching 2.5 ton heat pump. I've learned a lot here and am quite interested in HVAC. I watched the installer "make" the line-set, which was 3/8" liquid line and 3/4" suction. I watched him bend and fit the line-set, which was off bulk rolls of copper tubing. He made 6 blazed connections, 2 at the outdoor unit (heat pump), 2 at the indoor coil, and 2 more for the bi-directional dryer. NONE of these braze connections were done with a nitrogen flow through the copper - tubing was just full of atmosphere. I told him to get out the nitrogen and he told me it's not necessary. From what I have read, he was wrong. I watched a video on youtube where a Guy brazes with and without nitrogen and then shows all the black oxidized material inside the tubing where nitrogen wasn't used. So we gave them 50% down to do the job and owe them 50% more. We are concerned the installation was not done correctly (nitrogen not used). The rest of the install looks very professional. The brazing looks perfect. Will this or could this cause us issues down the road? The owner of the company of course wants his money and also agrees with his installer. We want to pay them if indeed we won't have consequences from the brazing done without using the nitrogen.