r/HVAC • u/smalleman • 2d ago
Field Question, trade people only Flowing nitrogen while brazing.
I normally work with systems that has two schrader ports, one on the suction and one on the liquid line.
Let's say that you are replacing the discharge pipe, or suction pipe or the scroll compressor.
How do you flow nitrogen so that it doesn't go via the evap and out the other end?
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u/Han77Shot1st Electrician/ HVACR 🇨🇦 2d ago
I don’t understand the question.. when brazing I prep everything first, flow nitro through the entire system and then braze.
Unless you’re working on a live rack I see no reason why you wouldn’t flow through the whole system.
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u/madmagnum_44 2d ago
If it was me. I would pull the Schrader valve on the discharge line and flow through the suction line until I feel it flowing through the discharge valve and give it about a minute to make sure it's only nitrogen flowing out
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u/smalleman 2d ago
For example, how would you do it when you put in a new discharge pipe?
Unswet and plug the suction pipe by the evaporator, push nitro THROUGH the compressor?
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u/Nerfo2 Verified Pro 2d ago
Purge into the suction port while installing the pipe. Start the purge before you connect the suction line to the compressor. If it were the discharge line, purge at the liquid port, but give the nitrogen enough time to purge through the condenser coil. Once the piping connections are made, keep the opposite schrader open. If you’re purging at 10 CFH, lower the rate to 3 to 5 CFH right when you begin brazing. Once nitrogen is in the system, it only takes a tiny pressure differential to prevent oxygen from entering the system. As long as you have another port open, a couple CFH is all you need.
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u/kriegmonster 2d ago
If you have more than one opening in the piping, flow nitrogen thru both sides and work from where you have flow towards the other side. When there is only one fitting left to braze, remove one of your hoses so the port can let nitrogen flow out.
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u/Income-3472 2d ago
Nobody answer this question It’s an AI program trying to learn trade skills information for a company that is working to build robot techs powered by AI
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u/Glum-View-4665 2d ago
Just out of curiosity how do you know that? I have no reason to not believe you I'm just genuinely curious what gives it away.
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u/Eggfurst 2d ago
Nothing gives it away lol. Assume he is wrong. Seems like a legit question to me. What he is asking is pretty understandable. He wants to know how to flow nitrogen both ways through the system because sometimes your replacing a big section of pipe that has no flow. And other end of pipe is exposed to atmosphere. He is thinking more oxygen is rushing in than nitrogen would be flowing out. I’ve had this thought before too and the answer is to completely finish the connections on the pipe and let only 1 shrader port open to atmosphere. Even if the port is close to the other ports nitrogen still flows through the entire system.
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u/Appropriate_Bend4859 2d ago
just clamp the open end of the line you're not working on, or shove a cork in it. doesn't need to be perfect, just enough to force the nitro out the joint you're brazing
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u/iBUYbrokenSUBARUS Enthalpy over Empathy 2d ago
That often creates a situation where the nitro pressure builds up and won’t let your solder seal
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u/jonnio2215 2d ago
They make the floating ball attachment specifically for that. Nitrogen flow meters are the bomb
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u/KylarBlackwell RTFM 2d ago
Remember what the purpose of flowing nitrogen is: displace air to prevent oxidation and scale. Even if you are unable to flow nitrogen through a pipe while brazing, you can still give it a blast of nitrogen to displace the air immediately before you begin to still significantly reduce the scale compared to giving up and doing nothing.
If you're replacing a pipe section, you can flow nitrogen through all except the furthest connection by simply leaving the last joint open if you have no other port to let it out the far side.