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  1. #1
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    Automotive AC compressor question.



    Hello
    My father in law's car is not engaging the AC compressor clutch.Without checking anything, he suspects that all the refrigerant has leaked away,thus preventing the pressure switch to close the clutch circuit.That is just an assumption,we've not checked anything yet (we are pretty busy),but theoriticaly,if that is the problem,this arises the question about how much oil i must add to the system?.I assume that together with the refrigerant,some oil is also leaking out ,so it must be added later,when recharging the system,but how do i know how much i need to put back in?
    As far as i know ,the oil in the compressor's sump is lubricating the bearings and etc. in the compressor's body,and only a small quantity is circulating in the system with the refrigerant,so only a small quantity must be added when charging system,but how much?
    Thanks in advance



  2. #2
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    Re: Automotive AC compressor question.

    Recommend that you take the car to a reputable car A/C garage. They will know the best way to leak test and repair your system.
    Mobile A/C at its best, see avatar.

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    Re: Automotive AC compressor question.

    I'll check the system for leaks by myself.I have the instruments-gauges,vacuum pump,recovery machine and i bought a UV dye.Checking and repairing the leak is not the problem.The problem is that i don't know how to determine how much oil i need to add.From my humble experience i know that,when i was recovering a system,some oil is getting out of the system too and later i drain it from the machine.This amount must be added back,but i don't know how to determine how much i must add in addition to this.

    hyperion,in our country the situation is different.Almost everyone "can" do everything .And that's where the headaches starts.You take your car to a "reputable" garage,and then as final result the best that you can get is the problem not sorted.In worst case you can get few more problems due to the "reputable mechanics"'s actions.That costs time,money,nervs and etc.I'm not an refrigeration technician,but it's very interesting to me,so i started to read some books,bought an old split air conditioner just to learn,measure things and to see in practice the things that i was reading in the books before.I like to learn .So i prefer to do it myself,but i don't have much experience,so i need a little help about this and that.If something go wrong,i\ll blame myself,not someone else and i'll not be so much frustrated like if someone else mess up my car .In our country we have a proverb-if you want to get your job done properly,than do it yourself.
    Thanks in advance

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    Re: Automotive AC compressor question.

    Well,apparently I'll take the trail and error challenge when no one wants to give advice.Thanks ☺

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    Re: Automotive AC compressor question.

    Hi Th.Mihov,
    Automotive AC is not definitly my speciality, the little I know is more on the "heavy" and industrial field.
    Anyway the AC in my car (Ford S-Max) broke and on the process of repair I noticed that the charge of R134a is 600 grams. No oil was added. Or maybe the gas already had some oil in it, that I don't know.
    I will try to ask someone and if I get something I will come back.
    Good luck
    CDuque

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    Re: Automotive AC compressor question.

    Th.Mihov,
    I also do not specialize in this area but can offer this.
    Apparently Model, year etc required to narrow it down.
    Remove compressor & drain all oil out of it, measure amount removed, compare to what it should be, then add correct amount.
    There is a possibility some oil will be in system.
    Can you see any oil loss from compressor seal or anywhere else?


    http://www.autototal.ro/dmdocuments/...hr%20Hella.pdf

    https://www.youtube.com/watch?v=TANldmkL0sg
    Last edited by RANGER1; 21-04-2017 at 11:50 AM.

  7. #7
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    Re: Automotive AC compressor question.

    Hi again
    The car is Chevrolet Aveo 2010.I have not cheked almost anything yet,but tomorrow or in Sunday i'll have some free time and i'll take a detailed look for trails of oil leaked oil.If there is significant oil leak ,it should have a debris on it,so it must be visible.I doubt it has a serious leak,because he found that the AC is not working,before few days,but he have not used it since the last warm days last summer,so almost half an year has passed.In addition,when the AC is not running,the oil should be settled down in the compressor and the drier,so when the refrigerant has leaked out,there should be almost no oil in the lines and etc. and thus little or no oil should leak out,or at least i think so
    After last night i'm sure that the reason for not engaging the clutch is the lack of refrigerant,because i went to the garage to get something,and when i saw the car i decided to open the valve caps and push the schrader valve to see how much force is required to push it back,and no surprise-almost without any resistance,so there is very very low pressure in the system -> no refrigerant .Tomorrow or in the next day i'll check to see if there is something visible.If i don't find anything,i will evacuate,add the UV dye and recheck after few days,but i also want to add a little oil "just in case".I think about 10ml should not be a problem.That's 1/20th of the all mount.After i find and repair the leak,i'll drain and measure the exact amount of oil in the system and will add the proper amount.Any problems in my plans?

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    Re: Automotive AC compressor question.

    Quote Originally Posted by Th.Mihov View Post
    Hi again
    The car is Chevrolet Aveo 2010.I have not cheked almost anything yet,but tomorrow or in Sunday i'll have some free time and i'll take a detailed look for trails of oil leaked oil.If there is significant oil leak ,it should have a debris on it,so it must be visible.I doubt it has a serious leak,because he found that the AC is not working,before few days,but he have not used it since the last warm days last summer,so almost half an year has passed.In addition,when the AC is not running,the oil should be settled down in the compressor and the drier,so when the refrigerant has leaked out,there should be almost no oil in the lines and etc. and thus little or no oil should leak out,or at least i think so
    After last night i'm sure that the reason for not engaging the clutch is the lack of refrigerant,because i went to the garage to get something,and when i saw the car i decided to open the valve caps and push the schrader valve to see how much force is required to push it back,and no surprise-almost without any resistance,so there is very very low pressure in the system -> no refrigerant .Tomorrow or in the next day i'll check to see if there is something visible.If i don't find anything,i will evacuate,add the UV dye and recheck after few days,but i also want to add a little oil "just in case".I think about 10ml should not be a problem.That's 1/20th of the all mount.After i find and repair the leak,i'll drain and measure the exact amount of oil in the system and will add the proper amount.Any problems in my plans?
    Sounds fair what you are doing.
    Nice to see if it does work by adding a bit of refrigerant first, as then you would have to investigate that problem.
    Hardest thing is to find leak, then repair it.
    If it was the shaft seal, then you would remove, drain oil, measure, replace oil charge.
    Oil charge may be stamped on compressor body somewhere.

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    Re: Automotive AC compressor question.

    Early today i went to the car and had a look around.No signs of any oil leak,as far as i can see without tearing apart the car.Static pressure readings - high 0 bar,low 0 bar .I know that is totally wrong,but because i don't have a nitrogen , i decided to pump up the system with compressed air to see how fast it looses pressure.The test pressure was arbitrary set to 13.2 bar and dropped down to little under 13 bar after about 10-15 minutes,so there's a relatively big leak in my humble opinion.Although i knew that i won't find anything this way,i decided to test line connections with soap water and sponge-nothing.Apparently the leak is relatively significant ,but not enough to inflate a bubble in the soap-water.Then i had evacuated the system for about 20 minutes,wait about 15,and then evacuated for about 15 minutes,to get the air and moisture out,and i quited because my father in law had to go to work.
    Tomorrow i'll evacuate again,because i think the vacuum will be gone ,add the UV dye+10ml oil,and charge the system with little amount of refrigerant, just as much for compressor to run without cycling on and off and than i'll look again for leaks with the UV torch and hopefully the leak is not in a very crummy place

  10. #10
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    Re: Automotive AC compressor question.

    You won't sea a oil leak on a car not enough oil in a system only place you can sea a leaksometimes is on a on condensor when it's been gases multiple times we pressure test at ten bar for minimum one hr if gauges drop at all you have a leak the vacumn test don't work on cars I've had leaks on cars then used a torr gauge and it's held a vacumn perfect on that model the condensor will be leaking or the pipes that go to condensor on O rings they bubble after twenty mins
    When you have traced leak and regas if o ring add 5 cc of oil if you fit condensor 20 cc of oil also watch the condensor fans as prone to failure on plug to fan we very rarely uv dye there is no need just patience ta charlie just as reference I would never send a vechicle out with a vacumn on ac circuit

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    Re: Automotive AC compressor question.

    Thanks everyone for the advices
    I just come from the garage.Since yesterday,the vacuum has dropped about half.I taught that it will be no vacuum after that large period of time,but i was wrong .Anyway,i evacuated again,put the UV dye,added about 300 grams of refrigerant,left the car working at about 2000 rpm,checked everything-no leaks.Waited about 1/2 hour-still nothing.After i disconnected the gauges,i checked the schrader valves with the UV torch,and because there was few drops of UV dye in the low side valve,i saw a little bubbles coming out of the valve,and nothing else.I was happy for a moment that i found the leak but,after i think a little,the plastic valve's cap has a rubber gasket on it,so although the valve is leaking,the cap should seal the system and not allow the refrigerant to go out,or i am wrong?.More precisely,my question is are these cap reliable enough to stop the leak thus this is not the reason for the refrigerant loss,or it is plausible the refrigerant to leak out from there although the cap?
    I told my father in law to drive some days and i'll recheck it again,because i doubt that is the only leak.

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    Re: Automotive AC compressor question.

    you need fix the leak in Schrader valve - you cannot expect plastic caps hold for pressure building up inside and start to leak very quickly. In hot summer time and > 30 degree C you have far above 5 Bar constant pressure over long time even on low pressure side in situation as parking car in sunshine.

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    Re: Automotive AC compressor question.

    I agree with that .Few hours later,i went again to the garage to do something,and i decided to look again-it still has bubbles.I have pushed the valve's stem down and no-more bubbles.Apparently there is a problem with the valve,and if i don't find anything else after few days,i would say that the problem is here,and maybe after the last recharge,last year,the schrader valve was not fully closed and little refrigerant was slowly leaking out until it's all gone trough the cap.This is the only possibility for now

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    Re: Automotive AC compressor question.

    The dye sits under the valve if not flushed through and leaks just keep your high and low side gauges open when running and flush through so uv dye is not just in suction valve seat then check valve caps are to keep dust out not to seal

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    Re: Automotive AC compressor question.

    I find car ac to be a pain,if it's family then it's different,most leaks are at the condensor or piping going to it,by using compressed air you are putting moisture into the system so by doing this you must change the drier as you said ofn is not available,shaft leaks on compressor are common if ac is not used for at least a week in cold weather ,if that's where you find the leak change the compressor it's not worth going down the road of changing the seal compressors can be sourced cheaply.

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    Re: Automotive AC compressor question.

    Quote Originally Posted by charlie patt View Post
    The dye sits under the valve if not flushed through and leaks just keep your high and low side gauges open when running and flush through so uv dye is not just in suction valve seat then check valve caps are to keep dust out not to seal
    I think it should be flushed,because i was stupid,and after evacuating the system,i first put the UV dye,and instead of charge with liquid refrig.,i charged it in gaseous form,so only about 60 grams were charged (surprisingly,enough to actuate the pressure switch,and start the compressor).Then after i started the engine and the compressor ran,i continued to charge as gas from the low side but it was very slow,and after some time the refrig. bottle started to freeze up and the process became even slower,so i put the bottle above the engine to warm it a bit and continued,but i was impatient and i decided to charge it in liquid form slowly by throttling the gauges (open valve for a sec,and wait few seconds,than again),so almost 100% some liquid refrigerant passed through the hose and the schrader valve,so i think it should flush the dye from the valves,or maybe not... .As for the caps,i also think that they could not withstand much pressure,so eventually they will leak some day.
    By the way before few hours i have checked again-still no leaks after 24h+ in the garage (the car was not used today)...
    Quote Originally Posted by cadwaladr
    I find car ac to be a pain,if it's family then it's different,most leaks are at the condensor or piping going to it,by using compressed air you are putting moisture into the system so by doing this you must change the drier as you said ofn is not available,shaft leaks on compressor are common if ac is not used for at least a week in cold weather ,if that's where you find the leak change the compressor it's not worth going down the road of changing the seal compressors can be sourced cheaply.
    In my humble opinion,i don't think that such amount of air and moisture can clog the filter so fast especially when the system is not running,and i released it soon and evacuated it right after that.
    And finally one question about operating pressures vs ambient temp.I saw in the web few tables that gives a general "normal" readings for given ambient temps and humidity.In my case the condenser is next to the cooling radiator (about 1cm),so it constantly heats up the condenser and pressures should be higher than that shown in the tables or not?.When i measured them,the ambient temp in the garage was 24C ,the suction pressure was about 2bar ,the discharge when the cooling fan was not running went about 17bar,when the fan was running it was about 11-12bar.I think the suction pressure is lower than normal,because the system is not fully charged,but the discharge seems to me little higher for undercharged system?.Despite of that it is only half charged it was cooling well (nice cold air from the vents)

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    Re: Automotive AC compressor question.

    And still nothing .I feel lucky,that that was the problem.Thanks to all for the hepful replies .Any ideas about my pressure consideration?

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    Re: Automotive AC compressor question.

    Quote Originally Posted by Th.Mihov View Post
    And still nothing .I feel lucky,that that was the problem.Thanks to all for the hepful replies .Any ideas about my pressure consideration?
    Does the information about normal pressures indicate RPM of engine.
    If you have not already, increase RPM of engine to get good airflow over condenser, the discharge pressure might look better.

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    Re: Automotive AC compressor question.

    Run the engine at 1500 rpm to get good refrigerant flow through the system.
    Mobile A/C at its best, see avatar.

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    Re: Automotive AC compressor question.

    Yep,my mistake.I have made the measurements at idle speed (about 850rpm).Tomorrow i will evacuate and recharge again,because i have not seen anything wrong yet .In a few days i will report back how is it going .Thank you all for the helpful replies

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    Re: Automotive AC compressor question.

    Quote Originally Posted by Th.Mihov View Post
    Yep,my mistake.I have made the measurements at idle speed (about 850rpm).Tomorrow i will evacuate and recharge again,because i have not seen anything wrong yet .In a few days i will report back how is it going .Thank you all for the helpful replies

    Everyone in your region is going to contact you on car air conditioning after this, as you will be the expert

    Do you have to remove all refrigerant, just top it up if necessary.
    Last edited by RANGER1; 29-04-2017 at 10:31 PM.

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    Re: Automotive AC compressor question.

    Quote Originally Posted by RANGER1 View Post
    Everyone in your region is going to contact you on car air conditioning after this, as you will be the expert

    Do you have to remove all refrigerant, just top it up if necessary.
    No doubt about that .As for the recovery-yesterday i accidentally found that my discharge gauge is loosen (it was glued with something like liquid PTFE),so there is a chance some air was in the system,so after i fixed the gauge,i decided to evacuate again just to be sure that everything is fine .
    Now at 24C ambient temperature and 2000 rpm my suction pressure is about 2 bar and discharge is about 16bar,when the fan is running,which i think are good readings

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