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    Optimum size Vacuum pump for Automotive A/C?



    Hello everyone,

    Iím a long time forum lurker, first time poster. Iíve been searching the forums and generally researching information, it really is a wonderful site, with masses of expert knowledge and experience.

    Now Iíve buttered you all up I wondered if I could ask my first question that I canít quite get to the bottom of by searching old posts, however I apologise if it has been asked and answered before but I have missed it.

    As per the thread title: What would be the optimum sized vacuum pump for the evacuation of vehicle A/C systems?

    After various readings, I've discovered the concept of too quick an evacuation causing the moisture to freeze rather than be removed.

    I was about to buy a Javac 141 5CFM pump but now I wonder if this would be too large for vehicle applications and I'm worried it may freeze the moisture in the system rather than removing it as a vapour.

    Could someone educate me please as to either an appropriate sized vacuum pump or a method for calculating/estimating the size of vacuum pump necessary for cars?

    Thank you very much indeed for your kind help.

    Regards
    Mark



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    Re: Optimum size Vacuum pump for Automotive A/C?

    Go for their smaller pump but buy a good vacuum gauge.
    Brian - Newton Abbot, Devon, UK
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    Re: Optimum size Vacuum pump for Automotive A/C?

    You have to be carefull with the vehicles nowadays as many a different issue
    1, modern vehicles hold next to no refrigerant some now only 325 grams nowadays so no massive issue there so small vac pump required
    2, normally most vehicles have had multiple recharging so a good vac is no issue
    3, modern cars use a slightly flammable refrigerant and it requires a special vac pump so u don't go bang
    4, lots of vehicles now only have one test point
    So providing it's a car and not a tank a twin stage 3 c f m with a digital torr gauge would do well I personally run a 8 c f m pump on vehicles as I do a lot of plant but you have one big advantage on vehicles you have a heater and a running engine to help heat the pipework evaporator etc and with o f n this sorts most moisture in a small amount on vehicles
    Before its even vac ed ta charlie

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    Re: Optimum size Vacuum pump for Automotive A/C?

    Hello,

    Thank you very much indeed to you both for your help and advice, I apologise for my delay in responding. From my searches of old posts, you both certainly know your stuff and are very experienced, you both come up quite a lot and I’ve already read a lot by you both.

    That is really interesting and helpful Charlie. You must have been working on cars for quite a while, is that what you do, cars and plant?

    So if I may go over a point in the original question – it’s about this business of moisture freezing with too quick an evacuation.

    Though it is raised in other posts and discussions as something to be aware of, is it actually a reality? That is, does it actually happen in practice? Or is it only really with massively over-sized pumps evacuating relatively tiny systems? Charlie, I would have thought that if it was a real concern it would have given you big problems if you are using a 8CFM on vehicle a/c? I guess it hasn’t given you any problems then?

    The thing is for just a little bit more money I can get a 5CFM size vacuum pump instead of a 1 – 3 CFM size pump. But then I don’t necessarily want to get equipment that is excessively over-sized or incorrect for my applications and that may cause me a problem.

    Thank you
    Mark

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    Re: Optimum size Vacuum pump for Automotive A/C?

    I wouldn't worry too much as you can only suck about 1.5cfm down standard 72" long gauge line.
    Mostly found in Oxfordshire, UK :)

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    Re: Optimum size Vacuum pump for Automotive A/C?

    My preference is the Robinair pumps as they have proven reliability and durability out in the field with us.
    Any pump you should choose should be rated to 15/20 micron / millitorr on factory rating.
    Always go the biggest pump you can, if you suspect high moisture in a system follow the triple evacuation method.
    Pump ratings are in free air and at the low ranges your molecular flow is very low, so a bigger pump gets you there quicker (time is money) Then way up how heavy the pump is to transport and store and choose a sensible size for you!
    Anywhere from 1 - 10 Cfm would be ok in your application, I would look at quality, reliability and replacement parts availability over size for small pump range.

    Additional
    We have a big pump on a trolley for the installation of VRF / VRV and industrial / large comercial plants and this is saving us a fortune in labour time evacuating big plants.
    I love the smell of Ammonia in the morning!

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    Re: Optimum size Vacuum pump for Automotive A/C?

    Quote Originally Posted by charlie patt View Post
    3, modern cars use a slightly flammable refrigerant and it requires a special vac pump so u don't go bang
    ta charlie
    Charlie I don't want to seem argumentative
    the point you make though is pure sales rubbish from the salesman trying to get us to replace our pumps!
    vacuum pumps are two stage vane pumps oil sealed with no real ignition source, even a sparking bearing is protected by lip seals and you would not be running your pump in this state with no oil.

    When pulling a vacuum you are not pumping refrigerant, any refrigerant pulled out of the oil would be in an over rich state as air had been removed first and would not ignite (see point of ignition above)
    amount of refrigerant would also be so small as to be purely theoretical.

    If you have nitrogen purged before vacuum as we always should, where is the flammable refrigerant?
    I love the smell of Ammonia in the morning!

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    Re: Optimum size Vacuum pump for Automotive A/C?

    I must admit, i was thinking the same as hookster, if a job is done correctly then there will be no refrigerant in the system when proceeding to the vacuum stage due to recovery and purge of the refrigerant first

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    Re: Optimum size Vacuum pump for Automotive A/C?

    Quote Originally Posted by monkey spanners View Post
    I wouldn't worry too much as you can only suck about 1.5cfm down standard 72" long gauge line.
    This is a genuine thought, not trying to be contrary, but if this is the case then does it mean then that the use of any pump greater than 1.5cfm is actually redundant?

    What I mean is if I have a 5cfm pump vacuuming a system with hoses that limit the cfm to 1.5cfm, then presumably there's no benefit with such a size of pump?

    What am I missing?

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    Re: Optimum size Vacuum pump for Automotive A/C?

    This guy has some interesting vids on vacuuming,

    https://www.youtube.com/watch?v=hCXNL0IWb1I&t=711s
    Mostly found in Oxfordshire, UK :)

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    Re: Optimum size Vacuum pump for Automotive A/C?

    Some twin systems have solenoid valves well some are a bit more of a eev on suction and discharge if your vacuuming without vehicle running and climate on you will either vac half the system or when you run it and valves open up what ever is in it is now contaminated or worse if your on a modern crysler running 1234yf you pull ur vac you switch on vehicle to warm up switch ac on woops you now have 255 grams of slightly flammable entering your vac pump this is why with the modern equipment on vehicles you have to be carefull you assume ur system empty and it may not be this is where the flammable gas comes from and as far as the pumps go I seen what happens to a class terratrac when some knob vac ed it after assuming it was on 134 when it was on yf the new pump was the least of his issue vac ed it switched on ignition of combine heard the pump change noise then saw the flames come out by the time he got to it there was a lot of fire damage to his equipment and combine

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    Re: Optimum size Vacuum pump for Automotive A/C?

    .

    Vac pumps come in multiple sizes but mostly only 2 main types.

    Single stage and two stage. What you need is a two stage with an interference between
    stages, sometimes called a ballast or the ballast?? With the ballast screwed in the pump
    works on both stages and pulls deep vacuum. With the ballast screwed out the first and
    second stage get interfered with and it won't pull as deep, as quick. You then screw in
    the ballast to finish off the deep vac.

    As foe flammable gasses, the Hydro Carbon course (propane, butane and stuff) teaches
    an exclusion zone of 3 metres form the vac pump to the electrical switch.

    If you plug the vac pump into an extension lead and then switch the pump on and off at
    the wall at least 3 mtrs away from the pump you can use any and all types of vac pump.

    So a good vac pump with a ballast and an extension lead for switching flammables.......

    Rob

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    Re: Optimum size Vacuum pump for Automotive A/C?

    So what happens when the brushes flash on the armature shaft when the slip ring gets a bit worn ? I have vac pumps that vent on the handle just above the motor surely anything like this is a bit silly ? When dealing with these gases? Also a lot of these pumps have the three pin kettle plug so if it gets kicked whilst on in a localised area surely this ain't good practice, going back to the original question for cars nearly any pump will do with the wide range of cars out there it's hard to be accurate the problem you have is whatever you work on there is a vast chance some very unqualified people has already been at it ie Halford self fill so whatever pump you use will be no doubt better than most of what's been on it already I'm still a believer of having the correct kit for correct job and on whatever flammable gas I'm on i shall still be using the correct kit it's all well and good until something goes wrong and you can spend years building a good reputation and lose it in seconds ta charlie

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    Re: Optimum size Vacuum pump for Automotive A/C?

    .

    The course teaches how to do it properly.

    Why would you be vaccing a system with refrigerant inside?
    The system should have been purged with OFN and possibly
    pressure tested with OFN.

    If the job is done correct there will be negligable amounts of flammable inside
    and that is with propane or butain so the new A2L low flammable gasses would
    be almost impossible to ignite.

    Rob

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    Re: Optimum size Vacuum pump for Automotive A/C?

    Thanks Monkey Spanners for the link, I did actually see your link in another thread while I was searching through older posts and they are a very good series of videos. It was a month or so ago and I must watch them again to see if it directly answers my original question, I can't quite remember, don't think it did though.

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    Re: Optimum size Vacuum pump for Automotive A/C?

    And thanks to the other replies too, its developed into a really interesting discussion with some valuable information contained in the replies

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    Re: Optimum size Vacuum pump for Automotive A/C?

    Rob the way u can have refrigerant in a vac pump is the new bmw crysler class kit run twin solenoids on twin and quad ac systems they two valves on a twin 8 on a quad totally isolate the pipes and evaporators on a twin or quad so on a 1234yf on a quad you reclaim refrigerant hp test then vac the problem being when you start car to warm cabin and switch on ac the solenoids open and approx 320 grams are heading for your vac pump the only way to open them is to energise ac or scanner so if your running a unsuitable vac pump it is surely possible things go bang if your using wrong kit it's going to end in tears this was my point in the beginning it depends what you work on but the days of popping a bit of gas into a modern vehicles is gone I'm afraid ta charlie

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    Re: Optimum size Vacuum pump for Automotive A/C?

    Quote Originally Posted by charlie patt View Post
    Rob the way u can have refrigerant in a vac pump is the new bmw crysler class kit run twin solenoids on twin and quad ac systems they two valves on a twin 8 on a quad totally isolate the pipes and evaporators on a twin or quad so on a 1234yf on a quad you reclaim refrigerant hp test then vac the problem being when you start car to warm cabin and switch on ac the solenoids open and approx 320 grams are heading for your vac pump the only way to open them is to energise ac or scanner so if your running a unsuitable vac pump it is surely possible things go bang if your using wrong kit it's going to end in tears this was my point in the beginning it depends what you work on but the days of popping a bit of gas into a modern vehicles is gone I'm afraid ta charlie


    The trouble with life is something always gets in the way and makes it complicated.

    I agree there are always systems and circumstances that are designed or accident
    that come along and disrupt normal procedures.

    Good practices are good practices and informing people of systems like this is important.

    You make good valid points Charlie and I was not trying to belittle them. The BMW sounds
    like a dream to work on, you lost me at the first twin quad .....

    All the best Rob

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    Re: Optimum size Vacuum pump for Automotive A/C?

    Calculation of Vacuum pumping capacity will require specification of internal outgassing rate or gas load at specified pressure and requested pump-down time.

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