How much refrigerant oil and freon to add?

Discussion in 'Discussion Forum' started by lookforjoe, Mar 7, 2020.

  1. lookforjoe

    lookforjoe True Classic

    Searched & found several threads that indicate about 1.5lbs (or 25-32oz in Larry's thread) - but not finding how much oil to add for a completely empty / new system

    3oz? 8oz? I dunno...

    Advise?
     
  2. Dr.Jeff

    Dr.Jeff True Classic

    Location:
    Sin City
    I'm assuming you are referring to your modified/custom AC system with the engine swap? If so, the proper amount of refrigerant for that will not be the same as for any original or standard system. With a custom made AC system you cannot go by the weight or specific quantity of refrigerant, it may be too much or too little - both of which will result in suboptimal performance. Instead the best method in a case like this is to go by measuring the temperature at specific points on the system while you add refrigerant. And those temps will tell you when it has the correct amount for that particular system.

    The measurement points are the two ends of the low pressure line between the evaporator and the compressor. Measure as close to the evap and compressor as possible, and when the temp at those two points become equal it is done. Also follow the pressures on your manifolds to make sure you do not exceed the safe limits as you fill it.

    As for the amount of oil, that is also a bit difficult to answer on a custom built system. The 'standard' method for a stock system is to follow the manufacturers recommended quantity, but that doesn't apply here. Another is to measure what comes out of the system and put the same amount back, but that also does not apply. Each of the major components (compressor, condenser, evap, receiver/dryer, etc) will require a specific amount based on their size. So one method is to compare the measurements (size) of those components to a chart to estimate the total amount of oil. Some of the components like the compressor will have specifications for the proper amount for that particular component model. You can find that on the compressor's manufacturer site. The rest can be estimated from the sizes. Note that most new compressors come pre-filled with oil, so take that into consideration. Make sure the type of oil you use is compatible with any existing oil in any of the components and with all the other parts of the system, as well as the refrigerant, that you have.

    Sorry this isn't a direct answer to your question, but honestly there isn't one if you are working with a non-stock system that you assembled. If it helps I can refer you to a couple of very experienced experts to consult...that's where I got this information.
     
  3. lookforjoe

    lookforjoe True Classic

    Thanks Jeff

    I think I can still go by stock capacity for oil though - mine isn't larger / more hoses, etc. Only real change is addition of Accumulator.

    For Freon, my plan was just to add less than factory, then check operating temp, just wanted some confirmation of R134a capacity there also

    Thanks for the tip on low side hose ends temp check :)
     
  4. For the Freon, can't you go by system pressure? I would think going with the stock amount of oil should be close.
     
  5. Dr.Jeff

    Dr.Jeff True Classic

    Location:
    Sin City
    Agree, if everything is pretty close to stock but not quite, I think I'd go by pressure for the refrigerant. The oil isn't quite as critical so stock should be fine, assuming you have the same compressor as a stock system. That's the biggest factor for the oil.
     
  6. kmead

    kmead Over half way.

    Location:
    Michigan
    As this is a different compressor from Fiat stock, I would look at other cars that share the same compressor. Is there not a spec for this compressor model?

    As for Freon I recall it being done by pressure measured while running. The system needs to be pumped down (ie vacuum) and add the refrigerant as you monitor the pressure in the system while running. I picked up a set of gauges when I had to add refrigerant to my van.
     
  7. Dr.Jeff

    Dr.Jeff True Classic

    Location:
    Sin City
    In the old days the normal method for filling a system was by pressure. But at some point that was replaced by filling according to weight (of refrigerant). I'm not certain why, but that is the standard technique used now. It might have something to do with the change in the type of refrigerant used for automobiles? Maybe the pressure method isn't as accurate with the newer refrigerants? I don't know. But when I do a modern car with R134 I use both methods; weight the amount that goes in, and monitor the pressures. Typically the "weight" method adds a little less than the "pressure" method. And in fact the pressure method often ends up overfilling a bit. When I do a older car that has a stock system and R12 then I go by pressure, because the correct weight isn't known (that wasn't established back then). But when I do a custom build system from a mix of new components and R134 I use the temperature differential method (described earlier), because that's what I was told to do by respected experts. But I honestly don't know why.
     
  8. lookforjoe

    lookforjoe True Classic

    I put about 4oz of oil in, after sucking it down for about an hour after verifying it held a vacuum. I then added 24 oz of refrigerant, but it seems that wasn't enough to turn the compressor on. I bypassed the low pressure switch & ran the compressor - to check that it would run. This is the current low pressure, so at this point I'll just add refrigerant slowly to get the low side to 35-40, I think that's about right.

    [​IMG]
     
    Last edited: Mar 8, 2020
    kmead likes this.
  9. Dan Sarandrea (Phila)

    Dan Sarandrea (Phila) Waitin' On Parts...

    Location:
    Philadelphia, PA
    If going by pressures, isn't there a correction for ambient temps? Here in the Phila/NJ area, it was pretty cold today but is supposed to warm up, probably likewise for your neck of NY.
     
  10. Dr.Jeff

    Dr.Jeff True Classic

    Location:
    Sin City
    Definitely compensate the pressure for the ambient temp. Some gauges allow that on the face readings, but they aren't always well laid out to be read that way. So using a conversion chart is easier in my opinion. You can find charts online.
     
  11. PV=nRT
     
  12. lookforjoe

    lookforjoe True Classic

    Actually it's all moot right now - I found one of my beadlock crimps is no good - same hose that I had had made elsewhere previously :(
     
  13. Dr.Jeff

    Dr.Jeff True Classic

    Location:
    Sin City
    There is a new style of AC hose ends that you can easily install yourself and they seal well. Uses Oetiker type clamps. The price is reasonable plus they are reusable. Take a look:
    https://retro-fitusa.com/
     
  14. lookforjoe

    lookforjoe True Classic

    Thanks for the link. The fittings look good - except for the length - I don't think I could make their #6 90ยบ MIOR work in this space - the upper fitting (under the rad support) is the problem :(

    [​IMG]
     
  15. Dr.Jeff

    Dr.Jeff True Classic

    Location:
    Sin City
    They are longer than regular fittings due to the type of hose attachment, with double clamps. When I get to that point I'll have to see how they fit my installation. But I won't be using any of the stock components, including the hard lines, so I may have more options.

    Another neat feature is the "universal" attachment for any ports, sensors, etc. Makes that aspect very flexible.
     
  16. Dr.Jeff

    Dr.Jeff True Classic

    Location:
    Sin City
    Today I had an interesting experience when filling a AC system. Although this was not on any of my X's, it does pertain to this discussion about how much refrigerant to add.

    We discussed the "pressure" method vs the "weight" method, and I noted that I typically monitor both and find the "pressure" approach seems to add a bit more than the "weight" method. Well today it was the opposite, the pressures came up before reaching the full weight capacity (by a couple of ounces). Granted there may be something contaminating the system causing the pressures to go higher than normal, but I don't believe that's the case. One thing that came to mind is the ambient temp is much lower today than when I usually do any AC service. Admittedly I usually only do such work when something has gone wrong, which inevitably is during the hottest part of the year. But this time I knew it would need servicing and wanted to get it done before the 112 degree heat hits (which is coming very soon). Using the standard ambient temp conversion charts to adjust the pressures, the cooler weather means a much lower pressure level compared to hotter days.

    Therefore it may be a case of "it depends". If you are servicing in cooler temps, then the pressure method may yield adding less refrigerant than the weight method. But if you are servicing in hotter temps, then the opposite may occur. This might be why the factories have gone away from using pressures and only go by weight. Perhaps it is more reliable under all conditions. I'll have to remember to ask this question at the next trade show when I have direct access to the country's top AC experts.
     
    lookforjoe likes this.

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