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General Compressor Oil Question

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  • General Compressor Oil Question


    I have a question regarding adding compressor oil that I've never fully understood.

    For a brand new A/C system which has never been charged/run before, is there any need to ever add an oil charge through the suction line port during system charging if compressor already has oil added to the proper level?

    For reference, my car is a 1966 Ford Mustang with OEM-style York compressor. The system will be charged with R-12 (and just in case anybody cares, I do have my 609). Therefore I will be adding mineral oil to the compressor prior to this. Is this the only place where oil ever needs to be added? I always just assumed that the 12oz cans of oil charge which are added through the suction port are for adding additional oil to an older system with refrigerant already in it. However, I want to be absolutely sure that I'm not missing something here, and end up burning out my compressor.

    Last edited by RJSalucci; 06-06-2023, 12:17 PM.

  • #2
    Well you are lucky, the old Yorks have a oil plug on the side of the compressor, and you can check the level with a
    dipstick. If your system is fortunate enough to have backseat service valves you can check anytime even if the system is charged.
    If the compressor has full load of oil, then no, you shouldn't need to add.
    To check the oil on a charged system:
    fully close the suction valve, leave the discharge valve open and turn the compressor to pump the refrigerant that is in the compressor out the discharge port, then close the discharge valve. To turn the compressor you can do it by hand or monumentally engage the compressor with the engine running.
    Now the compressor is virtually empty, so you can remove the plug and use the dipstick. Add oil as needed, then evacuate the compressor with a vacuum pump, then open the service valves and your back in business. One of the neat features on these old system.
    My 1992 Marmon was set up with a Tecumseh with service valves, and I would check the oil every so often.


    • RJSalucci
      RJSalucci commented
      Editing a comment
      Thanks for the info! Yes, fortunately I do have the back-seating service valves at the compressor, and will definitely be taking advantage of that feature. The fact that you can completely isolate the compressor from the rest of the system, and even remove it from the car without opening the system at all is pretty cool indeed! (granted you aren't removing it because of a compressor failure of course)

  • #3
    Does your new compressor contain oil??? When I've added oil to a new compressor, I first drain (through suction port) and measure how much oil is in the compressor. Then I add the correct amount into the suction side and manually turn the compressor drive plate slowly though at least 6 revolutions.

    I've also flushed a couple of brand-new compressors for my still-R12 truck as those arrived with PAG oil instead of R-12 mineral oil (when I was working I could tell in 5 minutes the type of oil with one drop).​ For those, I drained the PAG oil, added about 6 oz. R-12 mineral oil ​and manually turned the compressor drive plate slowly though at least 6 revolutions. Then I drained that and repeated that flush. Then I drained that second flush and added proper amount of R-12 mineral oil ​​and manually turned the compressor drive plate slowly though at least 6 revolutions, then installed the compressor.


    • RJSalucci
      RJSalucci commented
      Editing a comment
      Hi, thanks so much for the reply! That’s a lot of really good info. My compressor does not currently have any oil in it. So I’ll be adding that in the near future once I finish restoring my under-dash evaporator unit and a few remaining hoses.

  • #4
    One last thing... Anyone here ever had performance issues running an old R-12 system with a newer TXV valve designed for an R-134a system?

    I'm thinking that while I have my evaporator all taken apart, it would probably be wise of me to replace the TXV. The only problem is, my new valve is stamped 'R-134a' in teeny tiny letters on top of the diaphragm, and I imagine it would be very difficult to find a NOS valve from the R-12 days. Being that both refrigerants are fairly similar in terms of temperature/pressure characteristics, I would think that any TXV orifice sized for R-134a wouldn't have much of an issue with R-12. However, it would be good to hear what your guys' experiences have been doing this.

    Would I be better off just leaving the original TXV in there and hope for the best (I have no reason to believe that there's actually anything wrong with it other than the fact that it's very old)? I've heard there's a way to bench test them, but I've never actually tried it.

    Thanks again everyone for all the replies I've received so far on this thread. I very much appreciate your advice & expertise.
    Last edited by RJSalucci; 06-07-2023, 10:42 AM.


    • #5
      Most if not all Tx valves can handle either refrigerant as its job is to look at the outlet and inlet of the evaporator and limit the refrigerant so that it has all boiled by the time it leaves the evaporator. It doesn't care about the make up of the refrigerant only that it has boiled. What changes is the heat load on the evap, and that is what the Tx valve regulates for.
      Theoretically a Tx can stick or be plugged, but in fact there isn't much to go wrong unless the thermal bulb tube is broken. I have reused with good results, but I wouldn't hesitate for a sec over using the new one marked 134a.


      • RJSalucci
        RJSalucci commented
        Editing a comment
        Awesome. Thank you for the info. I'll probably just go ahead and install the new Tx valve and not worry anymore about it then.