Pulling Vacuum; Recovering refrigerant questions? (New to the trade, confused)

[Snowman84]

Hello all,

Question #1: When pulling a vacuum, is it ok to have the service valves on the condenser unit open. I ask this because I would think that pulling a vacuum on the entire system (evaporator coil/line set/condenser), would actually pull the oil that is stored in the compressor out, causing some sort of mess or possibly messing up the vacuum pump. Im sure the more experienced guys will laugh at this, but am I just over-thinking all of this?

Question #2: What exactly is the step-by-step procedure when sweeping a system(line set & evaporator coil, condenser service valves closed) with nitrogen? If after pulling a vacuum, you released a nitrogen charge into the system either on the high side or the low side, wouldn't the charge just stop at the expansion valve and not be able to flow all the way through? In my mind I thought the idea was to close off one side, charge the nitrogen in on the other side, let the pressure build, and then let open the other side releasing the nitrogen charge and blowing/sweeping out all the sludge/debris?

[beenthere]

Won't pull out the oil.

A low pressure will go through the TXV(even if its a balanced port TXV).

[HVAC/Stud]

I hope you are going to a HVAC school or learning from someone how to do HVAC. This is not a trade that you can do without training. If you have been to a school, get your money back.

STUD

[54regcab]

If you are installing a precharged condenser (most 410A condensers come with refrigerant), leave the valves CLOSED while pulling the vacuum.

[jatinder.bhargav]

Ans 1: If condenser is not precharged,then yes you can open all the valves. as vaccumm velocity is not that high,so it will not pull the compressor oil.

Ans 2: Pressure will go even if TXV is closed. Other is its good to put nitrogen from both suction & liquid ports.
b/w why you want to charge nitrogen after vaccumising?? not getting it.

[Snapperhead]

Hello all,


Question #2: What exactly is the step-by-step procedure when sweeping a system(line set & evaporator coil, condenser service valves closed) with nitrogen? If after pulling a vacuum, you released a nitrogen charge into the system either on the high side or the low side, wouldn't the charge just stop at the expansion valve and not be able to flow all the way through? In my mind I thought the idea was to close off one side, charge the nitrogen in on the other side, let the pressure build, and then let open the other side releasing the nitrogen charge and blowing/sweeping out all the sludge/debris?

When trying to blow/clean debris out of a system you REMOVE the piston / txv. Then blast the piping out with good pressure of nitro. IF you left the txv in there , it would catch all the crud and cause even MORE problems.

Sweeping nitro is NOT for cleaning out debris , its for brazing. Lets not get confused with blowing out lines like we did above.

Sweeping a small amount of nitro through the pipes while brazing keeps the black crust from forming inside the pipe that "could" ultimately flake off and cause a restriction down the line. You know how after you braze something it has that crusty black stuff that flakes off the pipe ? Well if you flow nitro inside pipes while brazing , it Stops the creation of crust inside the pipe. It will look shiny new inside after brazing. Pretty cool huh.

Now you hook up vacuum pump. After you have it vac down good , remove pump from hose. Hook up your refrig to hose , let the refrig fly.

[davidj001]

it works better if you use one of the "flushes" that is available now and i always install a liquid line filter/dryer just in case some thrash did not come out, and always use a scale when you charge the system it will save you headaches and time

[Snowman84]

Now see this is what I would have imagined, is that all of the crud would get caught up in the TXV. I've watched guys release nitro into the system without removing the TXV, and it never made since to me....but they were the "experts" so I didn't say anything. And that black flaking stuff is caused by oxidation I believe, so with nitrogen to displace the oxygen, then no oxidation....??

[VTP99]

Also research triple evacuation.

[GITONGA]

First of all remember you always install a filter driyer may it be a new install or a repair that involved exposing the unit to the atmosphere .then when you say sweep the unit with nitrogen it will depend on the task, did you have acid due to a burn out or you are trying to just get rid of foregn matter that might have entered the piping while installing that may be the little copper fragments you get when you debar the pipe or the black soot like stuff which you can avoid by running nitrogen through the system when you weld the piping i normally push though less than 5psi and that should keep your pipes clean after welding. then its a good practice to use the micron gauge and atripple vacuum .

[clokwork76]

You might be surprised at how bad some of the trade schools are out there and how little you really learn... Plus sometimes you wind up learning from guys that may be better techs than teachers, you find yourself in a place that you really have take it upon yourself to play catch up with your training. I have a feeling it happens a lot.

[clifpaul]

Yep

[GT Jets]

Now see this is what I would have imagined, is that all of the crud would get caught up in the TXV.

There should be minimal piping and brazed joints between the TXV and the filter/drier.

I've watched guys release nitro into the system without removing the TXV, and it never made since to me....but they were the "experts" so I didn't say anything.

Removing the TXV to purge with nitrogen? You lost me somewhere..

And that black flaking stuff is caused by oxidation I believe, so with nitrogen to displace the oxygen, then no oxidation....??

The black flaky crap is copper oxide and yes, it from the brazing process. Typically really exacerbated by overheating the joints during the brazing process. This can be virtually eliminated by brazing under a nitrogen purge.

If you don't ask someone on the job site questions, two things can happen (both negative).
1- The technician you are working with will assume you already know.
2- You wont learn a damn thing by simply watching and not understanding the processes.

If you are working with someone that wont take the time to answer your questions without belittling you, you need to work somewhere else, or at least with someone else.....

The only stupid question there is, is one that you answer yourself while asking it. (meaning you did not think it through before opening your mouth). I call it "Engage Brain Before Putting Mouth Into Gear"...

GT

[GT Jets]

First of all remember you always install a filter driyer may it be a new install or a repair that involved exposing the unit to the atmosphere .then when you say sweep the unit with nitrogen it will depend on the task, did you have acid due to a burn out or you are trying to just get rid of foregn matter that might have entered the piping while installing that may be the little copper fragments you get when you debar the pipe or the black soot like stuff which you can avoid by running nitrogen through the system when you weld the piping i normally push though less than 5psi and that should keep your pipes clean after welding. then its a good practice to use the micron gauge and atripple vacuum .

Invest in a flow meter... 5 PSI is enough pressure to keep your filler metal from getting good penetration, there should be no pressure to speak of entering the piping, just volume to displace the oxygen.

For smallish pipe (under 1 1/2") I typically use 5 SCFH, if anything over that I will use 15 or even 20 SCFH, the trick is to get in, get it hot, weld it up and get out...

It's funny, but you would be amazed at the amount of newbie techs we get that use the "if it's glowing it's flowing attitude". This is so wrong it's silly.

I have literally brazed 7 to 10 time the amounts of joints with one bottle of oxygen and acetylene than most apprentices and they almost always have leaks, with lots of practice comes a proven technique.

Good luck

GT