Using nitrogen while brazing and pulling a vacuum

[hvac meister]

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.

[gregp]

useless to have gauges on a system while you are evacuating. It's more of a convenience so you can add (weigh in) refrigerant then start the unit. If you could have just hoses with isolation valves so you dont lose your evac., a micron gauge and vacuum pump, you should be good to go. Unfortunately some techs still believe in the "I pulled it down to 30" method".

[ZeroTolerance]

250PSI of nitrogen is rather high. I usually only put in 150psi - 200max. (if I can't find leak with 150).

You're referring to nitrogen, vacuum, nitrogen, vacuum, nitrogen, vacuum, which is called doing a Triple-Evac. I don't always use this method unless I have burnouts or lots of moisture/contaminants in a system.

Venting the nitrogen isn't "cleaning" out a system. Depending on the amount of acid/contaminents in a system I will disassemble all components (evap and condenser) of a system and shoot nitrogen directly through them with some R-22 to clean them out well, then braze back in. Some also use RX-11 flush.

Using your gauges to pull a vacuum isn't recommended because it opens up the possibility of having more leak points in the system. Get Core Removal Tools, hook your Micron gauge to the side port of the core removal tool, remove the core, attach vacuum gauge directly to the rear of the core removal tool. Or you can get a vacuum tree and go this route. Use 3/8" hoses when possible. If using 1/4" hoses remove all the core depressors for a less restrictive vacuum. I recommend also getting a 1/4 tee so you can pull from both suction and discharge sides. Make sure you maintain your hoses and replace the seals every so often to prevent leakage.

When brazing you want to use a flowmeter to get your nitrogen at 1PSI to prevent oxidization.

If my memory serves me right, Copeland states that an appropriate vacuum is 750 microns

[hvac meister]

Wow... thanks for the quick responses. Sometimes because of space a core removal tool can't be attached. What then? Also, how best to test gauges for leaks?

[C Combs]

i have been going on a lot of warranty calls this summer because of restrictions and have found the strainer on these new 410a systems clogged up from brazing without nitrogen. I get out to the jobsite and find the condenser cycling on high pressure. hook up gauges and have gotten up to 700 psig and 26 degrees of subcooling. evacuate system and find time and time again the same restriction. All of these calls could have been avoided by displacing the oxygen in the lines with nitrogen while brazing. I believe this is gonna become very common until the installers start reading the installation instructions or take some advice. This problem does not occur immediatly after the install and sometimes the installers have already been let go or moved on to another company. As for me, I learned by their mistakes and use nitrogen while brazing along with installing the filter dryer just upstream of the txv as the installation instructions recommend. I used to install the filter dryer outside at the condensing unit, but after seeing this service call time and time again, I changed my habits.

[Damien]

Nitro flushing method helps push out any bad molecules still hanging on in the system.

Havent done a ton of vaccums, but this past week I have been on a the hunt for a better method.

Watch this series. Gonna be making a custom set-up soon for myself!
http://youtu.be/lxwsUz8Dg64

[hvac meister]

Thanks again for the input. The youtube series is good... I too will be making a custom recovery/vacuum set-up. It'll be nice to always have everything together when I need it.

[Rcb2875]

I wouldn't force high pressure through the condenser and release at high rates since it just blows out oil everywhere. In fact I don't like rapidly depressurizing any part of the equipment.

For general leak testing I only put about 50 psi in if I just brazed the joints. If it is a system that has a leak that I didn't braze I will up the pressure. I never take my regulator off 250 even while flowing for brazing. I find it just as easy to barely crack the valve until you can just notice flow from your open port. I have a separate quality valve after the regulator near the end of my hose for this and so I can shut off the flow quicker if I need to without having the bottle right under my feet the whole time.

Pressuring to 250 or whatever the systems test pressure is, is only for stability tests. If you have a weld that you are unsure of like on a king valve or compressor connection that was fubar'd and you had to try and fix it you might want to go to test pressures to make sure it will hold up.

Not sure what you mean by flushing nitrogen while pulling a vacuum but you might want to check your pumps positive pressure limit. They are generally designed to start at 0 psi and with a maximum of 5 psi before you connect and start them.

As for pulling a vacuum through the gauges, I use the SMAN3 which has a built in micron gauge and have found no problems using them. You just have to put a ball valve on the charging hose. With that said I am thinking of trying it the other way with a tree and separate gauge.

[Damien]

I should have made myself more clear.

Rcb, you're right, I certainly dont go blasting 250lbs through the system to flush. I blank off my pump and vacuum gauge, undo low side and flush away

And I dont ever go past 200 to leak check. I was taught 150 for 15min. One installer at my work goes like 350 on 410a systems. And another guy seems to think I need to leave it pressurized overnight:gah: So when I get there in the morning and obviously see a drop, when I already suspected a leak, I end up wasting my time, company time and customer time. I may be new, but I aint stupid!

[Rcb2875]

I should have made myself more clear.

Rcb, you're right, I certainly dont go blasting 250lbs through the system to flush. I blank off my pump and vacuum gauge, undo low side and flush away

And I dont ever go past 200 to leak check. I was taught 150 for 15min. One installer at my work goes like 350 on 410a systems. And another guy seems to think I need to leave it pressurized overnight:gah: So when I get there in the morning and obviously see a drop, when I already suspected a leak, I end up wasting my time, company time and customer time. I may be new, but I aint stupid!

LOL If I told someone that I was going to leave their system pressurized over night I might not get to come back or want to, the next day! Been hot as hell here ;)

One thing I have learned is that there are just about as many opinions of how to do something as there are techs.:grin2:

The very first guy that was trying to teach me how to do things ended up showing me so many bad habits that I never realized until I started being on my own and having to research everything for myself... now that was a wake up call :gah:

[Damien]

Most of what I have been learning during my first cooling season is trial and error, and lots of research.

Talked to my other tech about keeping his micron gauge as far away as possible from the pump and not in line between the pump and his gauge, would be a better representation of what was happening in the system and not what the pump was doing to the gauge. He told me I was wrong and it didnt matter:gah: I told him he needed to do some research and learn. Needless to say that was not a good day between him and I:whistle:

Either way, I try to seek out facts and go from there

[timebuilder]

I think this discussion belongs in pro residential.

[mgenius33]

I wouldn't force high pressure through the condenser and release at high rates since it just blows out oil everywhere.

Haven't we all done this once......once....

Not to steal Joe Piscopo's line in Johnny Dangerously...:grin2:

[Rcb2875]

Haven't we all done this once......once....

Not to steal Joe Piscopo's line in Johnny Dangerously...:grin2:

Especially when you decide.. why not blow off your face with the nitrogen real quick and open the valve a little more :mad: Yeah the heat really got the best of me that day lol

[PalmettoMaintPro]

LOL If I told someone that I was going to leave their system pressurized over night I might not get to come back or want to, the next day! Been hot as hell here ;)

One thing I have learned is that there are just about as many opinions of how to do something as there are techs.:grin2:

The very first guy that was trying to teach me how to do things ended up showing me so many bad habits that I never realized until I started being on my own and having to research everything for myself... now that was a wake up call :gah:

Too true. All the technical literature I read taught me to braze with nitrogen and then evacuate to at least 500 microns. The manufacturers of most pumps and gauge sets say the bigger the hoses and the less stuff in the lines i.e valve cores and valves and what not , the faster and more effective the evacuation. But all techs know about time constraints and the other factors that make exactly by the book impossible sometimes . The point about using a gauge set so one can just go ahead and weigh in the charge was a good offering of info as well

[kdb4]

Nice experiment, I always wanted to try that but didn't have enough pipe and fittings around to do a good test. Thanks.

[walterc]

We all have our methods.
Mine is 60# and 180# psi to test.
I assume since there were no leaks before i worked on it, the leaks will be in my brazing/connections, so I do around 60# first to check with soap for bigger leaks then 180# and soap it up for 15 minutes. I do not depend on a fall of pressure to leak test unless it's overnight. A tiny pinhole leak may not show in such a short time on a gauge.
When in doubt, I use the H10.