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    How deep a vacuum is really required.



    Ok, been reading about people's recommendations and obsession with extremely low levels. Question is, if your replacing component, say compressor, you reclaim etc cut out old part and fit new. It's my belief that during this process refrigerant will be boiling off from the oil and therefore no air will enter the system. Do you really need to pull such a deep vac?



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    Re: How deep a vacuum is really required.

    Pulling a deep vac proves that you have done a good job.

    Not pulling a deep vac means that you don't know how dry the system is and indicates a back of care.

    Do you have time constraints at your employment?
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    Always use a chart and be thorough, you are only as good as the last job

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    Re: How deep a vacuum is really required.

    Don't worry about how deep a vacc you need to get to Tony,

    You don't need to get the system in to a vacuum at all.

    Seriously, you don't.
    The only question is how long you expect your systems to operate after you worked on them.
    Modern synthetic oils that we use with our modern refrigerants are extremely hygroscopic, they also get acidic as soon as any moisture is introduced.

    So, the question is... How much acid do you want to leave behind in the systems you worked on?
    Generally accepted from most refrigeration oil manufacturers is a vacuum to 500 microns, providing that it is standing (=You can turn off the vacc pump and leave the system for 1/2 hour or so without there being a raise in pressure)

    After reading your post another question springs to mind. Have you got your Fgas ticket?
    If you do the reclaim properly, there wouldn't be any refrigerant boiling of from the oil now, would it?


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    Re: How deep a vacuum is really required.

    in the past when working on a split in a server room .
    i had problems get a low vac .
    in the ideal world i should of fitted a drier as the suction flare had being leaking .
    as server splits are thrashed to say the least . it was gassed up to get it running for the weekend .
    and still running to this day .
    the unit had run 24 /7 for about 6 or 7 years so 14 years nonstop .
    most splits get a rest when folk go home.
    nowadays, if not getting a good vac on a repaired system , i would call a halt and put a drier in .
    if still a rising vac .
    no doubt will get a call tomorrow telling me its gone bang.
    on a new system will still pull a good vac and do the rising test , always want to see the vac sit there for 30 mins , same with pressure tests , follow the rules . and leave site knowing you have done your best.

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    Re: How deep a vacuum is really required.

    The Viking, is a reclaim unit really capable of getting the system low enough to get refrigerant from the oil?
    yes I do have F Gas ticket.

    Brian, probably no more time constraints than everyone else, you know the system is dry because no air/moisture would have entered the system.

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    Re: How deep a vacuum is really required.

    a decent vac is sometimes a lost art, or where do u stop ? leave an old drier on? vac with a decent torr gauge and only carry on when a acceptable torr has been achieved I always go by a guide of 29.000 torr or more the component failed for a reason was it cause the last guy did not vac well or poor vac pump? I personally if fitting comp or whatever hp test then vac whilst vacing with four line gauges wire in the electrics or do your f gas paperwork by that time its vacing well if system good it will be ready anyway if not give it time never rush one of the most important processes in refrigeration

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    Re: How deep a vacuum is really required.

    Quote Originally Posted by tonyk View Post
    The Viking, is a reclaim unit really capable of getting the system low enough to get refrigerant from the oil?
    yes I do have F Gas ticket.
    At room temperature, refrigerant should be all boiled from oil, at vacuum level wich reclaim unit is capable to produce (at least -0,5 barg)! It is just matter of time.

    Brian, probably no more time constraints than everyone else, you know the system is dry because no air/moisture would have entered the system.
    You only know that system is dry enough, by measuring standing vacuum level! At 1000 microns you have 10 ppm H2O in system.
    Last edited by nike123; 08-06-2014 at 10:23 PM.

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    Re: How deep a vacuum is really required.

    Quote Originally Posted by tonyk View Post
    The Viking, is a reclaim unit really capable of getting the system low enough to get refrigerant from the oil?
    Nope, most are not unless you use crankcase heaters and a lot of time.
    However, all reclaim units are able to pull enough refrigerant out of the oil so that what is left boiling off is nowhere near enough to keep moisture out of the system.


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    Re: How deep a vacuum is really required.

    Quote Originally Posted by tonyk View Post
    (snip)you know the system is dry because no air/moisture would have entered the system.
    Sorry, but that is a rather an arrogant statement.
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    Re: How deep a vacuum is really required.

    If there is enough refrigerant escaping to stop contaminants entering the system how do you manage to braise the joint with pressure and toxic fumes escaping ?

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    Re: How deep a vacuum is really required.

    Quote Originally Posted by tonyk View Post
    Ok, been reading about people's recommendations and obsession with extremely low levels. Question is, if your replacing component, say compressor, you reclaim etc cut out old part and fit new. It's my belief that during this process refrigerant will be boiling off from the oil and therefore no air will enter the system. Do you really need to pull such a deep vac?
    If this was the case and refrigerant was boiling off, completely stopping air from entering system, it wouldn't take very long to pull a deep vacuum would it??

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    Re: How deep a vacuum is really required.

    As you will remember from your steam tables, water boils at 15 C at 2 Torr. If its colder, you'll need a lower pressure within the system to boil off the moisture. If its warmer, you'll boil the water (moisture) at a higher vacuum.

    The usual amount of time when installing is "until the drain is finished" - Hope this helps?

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    Re: How deep a vacuum is really required.

    Quote Originally Posted by Gideon Beddows View Post
    As you will remember from your steam tables, water boils at 15 C at 2 Torr. If its colder, you'll need a lower pressure within the system to boil off the moisture. If its warmer, you'll boil the water (moisture) at a higher vacuum.

    The usual amount of time when installing is "until the drain is finished" - Hope this helps?
    That is what I was always told.

    At 2 torr (2000 microns) with the ambient temp at 16 degC water can't
    exist inside a sealed system, but the colder the weather the lower the
    level of vac.

    Most good vac pumps should achieve 1/2 a torr (500 microns) and
    given enough time they will remove all the moisture. If given enough time.

    If you doubt your torr gauge or vac pump then you will never truly
    know if the correct level of vac was achieved.

    I like most people take the vac pump for granted, until recently.

    I have access to a number of vac pumps, all well maintained, with good oil and
    either brand new or less than a few years old, I also have a verity of torr gauges,
    both digital and analog gauge type. Just recently I have had no end of trouble with
    various vac pumps struggling and torr gauges not reading correctly. I've had no end
    of issues with gauge lines, especially the ones with the shut off valve at one end
    and then combinations of all three.

    If I have such issues with the access I have to countless pumps, countless gauges
    and countless gauge lines, what is the hope of one pump working correctly all the
    time when used by a typical fridgy?

    If I have that amount of trouble, when I have access to every make of pump and
    gauge then the chances of individual pumps and gauges playing up is probably higher
    than people imagine.

    So don't be surprised if levels of vac are not as low as you think, unless you are
    comparing your set up against a know working system??

    Regards

    Rob

    .
    .. ... -. .----. - / -- --- .-. ... . / -.-. --- -.. . / --. --- --- -..

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    Re: How deep a vacuum is really required.

    I get my guages calibrated by a deep vacuum place, had my vac guage tested to .1 torr I was amazed it would read that low!

    they used a turbo molecular pump and vapour difussion pumping system, neat stuff.

    as to OP as others said, proper vac is criticle.
    Now in Redvers Sask.

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    Re: How deep a vacuum is really required.

    Well, if you are brazing in a new compressor (or any brazing) you should purge with nitrogen (not mentioned by OP). But how many engineers do? I find I have to stand over them and even row with some of them to get them to purge with nitrogen. Right now, I cannot recall one that did this without being told.

    Another question: how many have a working Tor gauge in their van? I find I have to bring one along with me to make sure they do a proper vac and to avoid the fait accompli of 'glass got broken yesterday', 'it is in the other van', 'left it on yesterday's site' and 'other engineer has my tools etc etc'. Check for a rise? They are just thinking about getting the cheque.

    And who carried torque spanners? For sissies, right?

    They can all do this on the assessment but on a site it all gets forgotten by many of them. Well, at least the ones I come across (and I am not referring to most of respected posters here).

    And charge the earth for a day's work. At least do the job right, I say.
    Last edited by Makeit go Right; 03-07-2014 at 01:51 PM.

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    Re: How deep a vacuum is really required.

    Here's food for thought:
    Doing our practical @ CNWL many years ago, one of the faults was moisture in the system causing a frozen TEV. Titchy system. I forget what capacity they were, but definitely titchy.
    The lecturers later told us that they expected a small squirt of water inside would do it. They actually had to put a litre or 2 in before they got the TEV to freeze up!

    I honestly think that fridge systems are far more robust than we're taught.
    However, I don't think that's an excuse to ignore best practice!

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    Re: How deep a vacuum is really required.

    Sorry Mr Geezer,

    You sort of got a flaw in your reasoning.
    many years ago
    my bet is that those units were operating on either R12, R22 or R502 depending on application. Those good 'ol gasses operated on mineral oil that is so stable that you can store it 50/50 with water and as long as you only take the top half (the oil) out of the can the oil will still be OK.
    However, our modern refrigerants demands synthetic oil which is extremely hygroscopic (it absorbs moisture) and as soon as any moisture comes in contact with the oil it will be absorbed and the oil will become acidic...

    Do you want acidic oil pumped around in your system?


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    Re: How deep a vacuum is really required.

    You're absolutely right Viking.
    I should have said they were on R22 & mineral oil, my apologies.

    Nonetheless I still believe that systems can take more abuse that we might think. After all, we are taught best practice (I HOPE!) at college.

    Bugger, I have to spread the rep I'm afraid.
    Last edited by FreezerGeezer; 04-07-2014 at 11:37 AM.

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    Re: How deep a vacuum is really required.

    tev wont freeze but have a look inside the compressor mate, it never ends well for the system as a whole.
    Now in Redvers Sask.

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    Re: How deep a vacuum is really required.

    <i><b>FreezerGeezer: "I still believe that systems can take more abuse that we might think."</i></b>

    I am not so sure customers would want their systems receiving ANY abuse. They spend a whole lot of cash for the thing and they want it to work properly for the full expected life. And that means installed correctly.

    And I pay the engineers to install it correctly per the manufacturer's manuals and good practice (including a proper vac). And if I catch any engineer abusing the kit that I just spent £100s and £1000s on, he'll be off the site in minutes.... and he can forget about his invoice because I will use his pay to get it done right.

    I can understand a plumber talking like that, but a trained aircon engineer is a little shocking. (I'm assuming you are trained and some years of experience, yes?) Strikes me you are causing a whole lot of damage to your customer's aircon kit. You have heard some facts above but still stubbornly going to continue in your ways, by sounds of it. That is sad.

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    Re: How deep a vacuum is really required.

    No no no, I obviously haven't been clear enough.

    You didn't used to work for major manufacturers if you were a bodger.

    Ok, the water in the system: that was a test, set up by the lecturers at college, as part of the practical exams for my class. Obviously you don't want any water in a system - I was just trying to show how what we are taught, or think we know isn't always accurate / right!
    If you haven't seen the old setup at CNWL (aka Dollis Hill, Neasden) the practical 'lab' was made up of Independent bench mounted Bitzer condensing units - 2 pot, I really can't recall the capacity, with a Russell cold room evap. mounted a meter or 2 above each one.

    Now, I don't know how knackered those setups were by the time my class was there. I don't think the lecturers had tried this before because they were as surprised as anyone how much water it took to show up @ the TEV. I was a student, so for all I knew they were about to scrap the systems in that lab. & didn't care about possible acid build up.

    By able to take abuse, I mean that these machines are tougher (ie, not as delicate) than we are at first led to believe. I DO NOT condone deliberate abuse. I guess I should have been a bit clearer.

    For example, we are taught never to charge liquid directly into a compressor suction because you will damage the valves (recip's, obviously). Either charge vapour (where possible) or use a vaporiser we are told. However, in the field every engineer I worked with used their gauge manifold to throttle the liquid. Vapour charging takes too long (as in, the customer won't pay for it) & done carefully, there is no danger of liquid slugging.
    Look back in the forum, perhaps the archives? There's at least one example of a scroll running backwards for six months & surviving.
    How many examples are there on the net, of rusted out, corroded, knackered looking equipment still managing to do some work?

    Yes, I do proper vac's when permitted by my employer. Splits as an example, usually only get a single vac to 500um or better on installation these days due to commercial pressures. Somehow they usually survive.

    Yes, I'm trained. Pretty well trained, in fact, and experienced. I came into the industry at a time when vac pumps were rare - there were 2 nationally in the manufacturer I worked for, both owned by Operations, not Service - and reclaim units had oil - we usually built our own. Purging was illegal I think, certainly not allowed, but still happened on smaller jobs as supermarkets wouldn't wait.

    So, Makeit go Right, why do you think I'm a bodger, exactly?
    And what on earth makes you think I diagree with the correct procedures given in previous posts? I suspect you didn't read the last line in my post - 'no reason to ignore best practice'?
    Last edited by FreezerGeezer; 04-07-2014 at 11:28 AM. Reason: Added the rest.

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    Re: How deep a vacuum is really required.

    Going back to the original post, if you are changing any component on a sealed system, the replacement will either be pressurised with OFN or "off the shelf."

    After reclaiming refrigerant and the system is opened, there might be a slight positive pressure.
    As the gas falls due to it's density and wafts out... Something has to balance the refrigerant loss.
    In comes the ambient air.
    To the optimist, the glass is half full. To the pessimist, the glass is half empty.

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    Re: How deep a vacuum is really required.

    Quote Originally Posted by The MG Pony View Post
    tev wont freeze but have a look inside the compressor mate, it never ends well for the system as a whole.
    Ok, it became blocked by moisture freezing in the orifice to be accurate. Sorry, another instance of not being clear I'm afraid.

    We had it happen for real at Tesco's Paddington (iirc) where there'd been a negative pressure leak. A few weeks of pouring hot water on TEV's & changing drier cores later, we'd got the moisture content to acceptable levels - as defined by my bosses, I was a youngster in Service then & did what I was told.

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    Re: How deep a vacuum is really required.

    I do lots of deconstructive analysis of failed systems (How I learn) and I love to get the history and story of the equipment.

    an old R12 system with high moisture (Not enough to freeze any thing up solid) it ate tevs for breakfast, drew enough current to power a 3rd world nation, and heated the building, but it kept the room cool so they kept it (3kbtu/h bty) nice big clean condenser, apon cutting open the compressor it became clear why so many issues the rust and sludge in it was mind blowing, the fact it even managed to spin up was amazing.

    basically any amount of moisture is bad, sure it will work for a while, but not for the long haul, I see fridges around here made in the 1920ies with sulfur dioxide still running and in use in some barns! Why? Becuase impeccable practices and workman ship. even some seriously old fridges at the dawn of r12 still humming away.

    when employers ask me to cut corners I tell them no, if they want a hack they can fire me and get one, but I will not do it, for one I will not have my name nore my effort attached to any thing less then a perfect job don to the best of my knowledge and ability will allow.


    in the end there is no maintenance like preventative maintenance, and that all starts with us for that first commissioning! We determine how long and how well it will run second only to the manufacturer
    you where clear, I was further clarifying that inferring some thing on a short term test on a class room system fails greatly when looked at over all life cycle, add in new oils and what have you it is totally irreverent that little experience in the class room.

    So it all ways comes back down to you just have to do it right, deeper the vac the better no matter how you slice it, as drier it is and free of trace contaminant gasses the better it will be for the systems life. Same with brazes, I all ways clean and sand all pipe joints to ensure a good solid joint, I all ways sweep with N2 when brazing, and all ways give it a good dry ofn2 purge befor starting the vac (To remove any moisture laden air) and I'd sure how any here do the same, as a customer I'd be soding well close to homicide if I caught a guy working on my gear with out doing any thing but the best practises
    Now in Redvers Sask.

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    Re: How deep a vacuum is really required.

    hi all
    reading the threads above it seems some of you should not have an f gas ticket
    or be classed as engineers simple as that if you cant decant a system proberly to below 10"hg
    or dont know what moisture in a system can cause then you are in the wrong trade or have not been trained right

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