Flowing nitrogen

[Shophound]

Originally posted by oilman52
Question....isn't todays solder strong enough to use on AC system? I can see brazing 2 different type metals but is it necessary to braze copper tubing? Not being a smart a@@,just want to hear your opinion.

Refrigerant lines are subject to conditions that water pipes aren't, for the most part. Rapid changes in temperature and pressure, and vibration. Therefore, the high strength of brazed fittings is best. I've seen soft solder used on refrigerant lines fail badly. I've also busted loose more than one water pipe that had a marginal soft solder joint...a wonder it didn't break on its own long ago.
I also would be leery of slapping flux onto lines that are supposed to be as free from contaminants as possible on the inside surfaces.

The last reason is why nitrogen is flowed during brazing operations. It minimizes oxidation of the inside copper pipe face when it is heated.

[oilman52]

You let nitrogen flow thru the lines as you braze. Do you let it trickle thru or do you let the nitrogen really flow? When you close the system up on the last braze,is the amount of nitrogen in the lines enough to stop flaking?

[oilman52]

I have used solder(silverbrite) in the past and haven't had any complaints. Old timer told me the old solder didn't have enough silver content or strength.

[HVAC Pro]

The mere presence of nitrogen or any inert gas is enough to prevent oxidation. It hardly needs to be flowing at all. Just enough inert gas to displace the oxygen will do the job.

[oilman52]

So HvacPro I could close the whole system up and trhen braze as long as I have nitrogen in the lines? You guys might be saving me some call backs.

[HVAC Pro]

Nitrogen is usually setup to "flow" through the lines. Otherwise, there is no way to tell if all the lines are subjected to nitrogen and not air. A very, very small amount needs to flow out of the system. I usually connect the tank to the vapor line at the outdoor section and pressurize it so that it very slowly comes out of the liquid line service valve with the shrader removed. Too much pressure and the nitrogen will blow the liquified brazing material out of the joint during brazing and create a leak. Flowing into vapor line allows the nitrogen to bypass the indoor metering device so that you don't have backpressure building while brazing. I also allow it to flow until the joints cool down. AC systems love nitrogen. It also speeds up the evacuation process as nitrogen is a good drying agent.

[tinknocker service tech]

stay brite is the only low temp solder i know of aproved for refrigerant lines and should be used with stay clean flux. their may be others but havent heard of any yet
you dont need nito because the melting point is low and flaking does not ocure. very little flux is needed and works well. by memorie it will hold 10,000 lb and hell i forget the vibrations. compressors should be brazed but have seen very few dummies solder them to
if nitrogen is flowed with staybrite the solder will be pushed out and not alowed to flow into the fitting properly

[toyotatech]

Drcustom thanks. Believe it or not, I have only obtained three bids, all from very well established, reputable companies, no hacks even considered. I chose the one to use because they sounded more knowlegeable and professional than the others, answered my questions competently and courtiously, did not push variable speed over the phone without seeing my house and ducts, did not push any one brand very hard. They insisted on performing a heat loss/heat gain calculation, and a ductwork evaluation. They were willing to install almost any brand equiptment if I had a preference for a particular peice of eqiptment, for whatever reason. This is the company that I have the most confidence in. They just so happen to be the most expensive, but not by a lot. I am willing to pay a premium for the piece of mind that my system will most likely be a nice clean install, installed by techs with experience, and that will hopefully be as trouble free as possible for a long time. Obviously price is not the sole motivation of every homeowner's decision.

Thanks for everyone's input, I appreciate the opportunity to participate in this informative board.

[johnl45]

Buy American!

[oilman52]

Thanks HvacPro. Next time I will try brazing instead of the Stay Brite. MAPP gas should get enough heat for brazing am I correct?

[601fitter]

Actually mapp gas is a little light on the heat for brazing.. I just did the system in my house and tried mapp gas in my home soldering rig, but had to get my oxy acetelene bottles to finish. Maybe your situation is differnt but that was my experience.. A B tank with a turbo torch would be ideal I think.
Lar

[ddsmith60]

I agree with 601fitter. Mapp gas alone did not have enough heat to flow Silverflow into the joint especially where there was a large heat sink. The first joint at the evap and suction valve. I guess with the 7/8" copper drawing heat away, the Mapp gas torch just doesn't have enough heat output. I bought a Mapp gas/ oxygen setup to see how well it works. I guess I should have Oxygen/Acetylene outfit but did not have the need for one yet. I cut with a plasma cutter when I need to cut metal. Maybe I need to buy more stuff.

[mark beiser]

For your first post, you revive a 3 year old thread?

Nice start!

[ddsmith60]

My bad Mark. I guess the new guy should shut up and go sit in the corner. In my past life I worked A/C and R in the Navy. Way bigger than this little 3 ton I just put in. It is nice to have a place to catch up a little when I need some information from the professionals. I've got to hand it to you guys. I don't think I would like doing this every day. So, I'll just go back to operating reactors for a living. It's easier.