Doesn't it help absorb moisture, flush contaminants, and ready the system for soot free brazing?

I was under the impression that the benefits are great and varied, and not doing it was akin to major malpractice. A sign of gross incompetence or blatant disregard for the property of others.

 

The use of nitrogen while brazing is critical. It removes atmospheric air from the lineset, which contains moisture and oxygen. The oxygen causes oxidation inside the lineset which is a contaminent and can clog TXVs. Failure to trickle nitrogen through the line set may not cause any immediate problems on new equipment startup, but can cause early failure on metering devices.

Adam

 

http://www.youtube.com/watch?v=3uP-eb8Zz08

 

Dry nitrogen can be used to keep the atmosphere pushed out and clean the lines.

A vacumm pump can only remove the vapor state substances so dry nitrogen is used to push out noncondensable contaminants from within the system.

Example: Motor burnout occurs while compressor is running. Contaminants are known to be in the condenser. The motor is removed and the liquid line is disconnected where the liquid line filter drier will be installed later. Nitrogen can then be purged through the liquid line toward the compressor and discharged out the discharge line before the compressor is connected.

During triple evacuation nitrogen is purged into the system to absorb and mix with other vapors. Also compressor cylinders can trap noncondensable gases and moisure. So under certain conditions a technician will quickly run a compressor when the system is charged with nitrogen to clear the cylinders.

During brazing a small amount of nitrogen is bleed throughout the system to displace the atmospheric air which contains moisture and oxygen. This practice almost eliminates the formation of oxidation inside of what you are brazing. Check out this link http://http://www.youtube.com/watch?v=3uP-eb8Zz08 about brazing with or without nitrogen.

I'm sure there are other reason to use nitrogen but these are the reasons I've seen. Hope this helps.

 

Nitrogen doesn't absorb any appreciable amount of moisture when used in a system.

Other than that, all other data is accurate.

 

Then the idea of a triple vac is mute.

I put in a counterflow furnace, cleaned + reused a lineset, new coil and AC. Put nitro in for overnight.

I always have nitro in the system to sit overnight on my first day of a multi-day job.

It pull down to 250 microns in half the time with a overnight nitro than without.

 

Nitrogen charge for air freight

Probably not too many normal people use air freight for air conditioners, but for various reasons I do it frequently. It's not legal to air ship a pre-charged unit from or within the US by air. We recover them and then add about 5 psi of nitrogen for shipping this way.

 

I use nitrogen for blowing out lines/coils, and as an inert gas bleed while brazing. The latter is far more critical now with POE oil systems than it used to be.

 

I dont understand this idea that nitrogen "absorbs" moisture. Nitrogen is a base element. Moisture (obviously) is H2O. The only way nitrogen could absorb it is if some kind of chemical reaction took place combining the nitrogen atom to the water vapor molecule. So far as I know, this isn't chemically possible (although I am not a chemist so maybe it is.), so where does this idea come from? The only thing I can think of is that since nitrogen replaces moisture laden air inside the line set maybe people mistakenly believe that it absorbs the moisture when actually it is replacing it....

thoughts?

Adam

 

The nitrogen will dry the system, but not because it abosrbs the moisture or reacts with it.

Say you had a 1 cu.ft container filled with air at 0% RH. Then say you evaporate 1 oz of water into it. What you have is:

1 cu.ft of air with 1 oz. worth of water vapor in it

Now, start adding nitrogen. We start at 0 psig (14.7 psia). For every additional 14.7 psi the gauge reads, you have basically added another 1 cu.ft of gas (ideal gas law, assume that temperature is constant). Say we pump it up to 45 psig. This means we have:

1 cu.ft air + 3 cu.ft nitrogen + 1 oz water vapor

The water is still there, but is now more diluted

Now, nature likes to even things out. This means that the water is not going to stick to just the air, but will diffuse thoughout the space (as will the nitrogen).

Now, let's empty the system. The pressure is going to come down from 45 psig to 0 psig. There will be 1 cu.ft left at 0 psig, but guess what? What is left will probably be 0.75 cu.ft of nitrogen, 0.25 cu.ft of air, and 0.25 oz of water vapor. This is because everything in the container was in equilibrium and when you empty the system, you are removing a mixture (air, nitrogen, and water vapor) and not just removing the nitrogen or just the air by itself.

If you went to 90 psig, then you would have something like:
1 cu.ft air + 6 cu.ft nitrogen + 1 oz water vapor

So you can see how you can dilute the mositure as you add nitrogen to the system.

If you left the system open after you empty, it will then go back into equilbrium with the outside air (nitro leaves and replaced with air, mositure content equals outside air).

So, I can see triple evac could help. However, with the time spent filling with nitro several times, you could have been pulling your single deep vacuum during that time, and may be better off. In a large system or one that may have oil with mositure in the lineset, use of a triple evac may save time.

 

I look at it as the nitrogen is pushing the air out of the system.

 

My understanding as far as removing moisture with nitrogen would be this. The nitrogen has such a low moisture content the moist air in the system would transfer to the dry nitrogen. Not chemically but hygroscopically. just my:.02:

 

That makes good sense, as does the idea of increasing the volume of gas in the space while the water content remains fixed...

 

To my understanding from what i have been told, a triple evac speeds the process to a deep vacuum. The deep vacuum would depend on other forces such as clean vacuum pump oil, tight system, clean vacuum rated hoses with good seals, tight gauge manifold set, and a pump that can pull into low vacuums.

 

GN2



using nitrogen ensures there will be no moisture in the system.

 

nitrogen displaces the air which holds some water, deep vacuum pulls it out of the oil.

 

You know how brazing a line always creates that black flaky crust on the pipe? You dont want that inside of the pipe. Running a little Nitrogen in the pipe stops this from creating while brazing pipe.

 

gezzz, hasn't this subject been beat to death??

:deadhorse::deadhorse::deadhorse:

 

I was at the Dermatologist a couple of weeks ago. He wanted to freeze a couple of places on me. Pulls out a Pony Bottle of liquid Nitrogen, that was wrapped in a sock. After I left, I'm thinking, "Can you imagine taking a small bottle in your tool bag to a big RTU or Chiller on the roof, rather than dragging that 90 cu ft up on the roof."