OK, let's say I have a leak. Some amount of refrigerant has leaked out.
If the leak is in the liquid part of the circuit, some oil has come out with the refrigerant. If it's on the vapour part, would oil mist still leak out? (Presumably it must, or the UV dye wouldn't work on leaks in the vapour part.)
I do a recovery. I haven't yet bought a recovery machine, but let's assume I get one with a distiller. The recovery returns 3oz of oil. Presumably that's not all of the oil in the system: some will be left behind when the last of the refrigerant boils and turns to gas during recovery, right?
So how do I know how much oil is in there?
Or, if I do the recovery with a non-distiller machine, then I have to do it slowly enough to leave all the liquid (and oil) behind. But I still don't know how much leaked out, so how do I know how much is still in there?
How do I know how much oil is in my A/C system?
I’m not an expert, but you might just have to flush the system so you can completely refill it with oil if you’re unsure. I didn’t flush my system doing a R134 conversion, but I did thoroughly drain the pump which should theoretically house most of the oil. I haven’t had any issues but YRMV
‘83 Platinum N/A 944
I found some references to "residual oil" amounts of specific components. I guess these are one of the things in the "updatable database" that the all-in-one service machines talk about. (You just have to work a little harder with Google, though AI narrows that gap considerably.)
Another source gave a rule of thumb: add 1oz for the leak and 1oz for each component you replaced.
Another source gave a rule of thumb: add 1oz for the leak and 1oz for each component you replaced.
'87 944 NA
'68 Series 2A, '96 E36 M3, '02 Vanquish, '15 Flying Spur
'68 Series 2A, '96 E36 M3, '02 Vanquish, '15 Flying Spur
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Tom
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I don’t know of any definitive way to tell exactly how much oil is in the system. Fancy A/C service equipment can tell you how much oil was removed during recovery — so you can replace the same amount — but that doesn’t really tell you how much was in there in total, or whether that amount was correct.
Griffiths told me that, when starting dry and converting to R134a, he uses about 5 to 6 oz. of ester oil total in the 85.5+ cars. The factory literature seems to suggest more like 4 to 5 oz. (PAG) when converting to R134a, but I went with Griffiths’ suggestion as the voice of real-world experience and haven’t had any problems — with vent temps in the 30s to boot. The early 944s apparently take more oil, according to the Porsche TSB excerpts below.
I think the best you can do is keep track of how much oil was put in when the system was dry, and then try to maintain that same total whenever the system comes apart. For the compressor, you can pour out the oil and replace roughly that same amount, assuming the level was right to start with. For the evaporator, receiver/drier, and condenser, Griffiths said to add back about 1 oz. for each of those components you replace, since the old parts tend to retain roughly that amount. Maybe add a smidge for any lines you replace too.
If you have no idea how much oil is in there, I think the only way to have real confidence is to drain the compressor, install a new receiver/drier, flush the evaporator and condenser, and then refill the system to your desired total. That’s just my shade-tree mechanic approach, of course — curious if @dr bob has a more dr bob-ish way to think about it?
Griffiths told me that, when starting dry and converting to R134a, he uses about 5 to 6 oz. of ester oil total in the 85.5+ cars. The factory literature seems to suggest more like 4 to 5 oz. (PAG) when converting to R134a, but I went with Griffiths’ suggestion as the voice of real-world experience and haven’t had any problems — with vent temps in the 30s to boot. The early 944s apparently take more oil, according to the Porsche TSB excerpts below.
I think the best you can do is keep track of how much oil was put in when the system was dry, and then try to maintain that same total whenever the system comes apart. For the compressor, you can pour out the oil and replace roughly that same amount, assuming the level was right to start with. For the evaporator, receiver/drier, and condenser, Griffiths said to add back about 1 oz. for each of those components you replace, since the old parts tend to retain roughly that amount. Maybe add a smidge for any lines you replace too.
If you have no idea how much oil is in there, I think the only way to have real confidence is to drain the compressor, install a new receiver/drier, flush the evaporator and condenser, and then refill the system to your desired total. That’s just my shade-tree mechanic approach, of course — curious if @dr bob has a more dr bob-ish way to think about it?
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