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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Finally getting back to this project. Car is a 1996 BMW M3.
I put the manifold gauges on it. As suspected, bone dry.
I pressurised it with an Azoidro canister (N2/H2) and spent some time with a sniffer. Everything seems tight except the condenser, which has a leak big enough to hear it hissing.
So I need to change the condenser (and of course the receiver/dryer). I might as well do the service ports as they're easy. And of course the o-rings on the condenser, receiver/dryer and service ports.
But then it gets trickier. The hoses/lines are 30 years old. But they look OK, and they don't leak. Still in the bathtub part of the reliability curve? New ones are going to run about €1000.
If I don't replace the hoses, I'll add 2oz of PAG 46 (1oz for condenser and 1oz for receiver/dryer). If I do replace the hoses, I'll add another 0.5oz.
I put the manifold gauges on it. As suspected, bone dry.
I pressurised it with an Azoidro canister (N2/H2) and spent some time with a sniffer. Everything seems tight except the condenser, which has a leak big enough to hear it hissing.
So I need to change the condenser (and of course the receiver/dryer). I might as well do the service ports as they're easy. And of course the o-rings on the condenser, receiver/dryer and service ports.
But then it gets trickier. The hoses/lines are 30 years old. But they look OK, and they don't leak. Still in the bathtub part of the reliability curve? New ones are going to run about €1000.
If I don't replace the hoses, I'll add 2oz of PAG 46 (1oz for condenser and 1oz for receiver/dryer). If I do replace the hoses, I'll add another 0.5oz.
'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
I did a lot of googling on the hose issue.
AI, of course, has an opinion, but with limited references so I don't trust it.
Most of the "well seasoned" folks race, and of course their opinion is that the whole system belongs in the bin.
Of those that don't race, the "well seasoned" opinion appears to be: AC hoses are not maintenance items. Replace when they start to leak, not on a schedule.
So that's what I'm going with. I ordered just the condenser and receiver/dryer.
(And I guess I owe AI an apology: that was its opinion from the start.
)
AI, of course, has an opinion, but with limited references so I don't trust it.
Most of the "well seasoned" folks race, and of course their opinion is that the whole system belongs in the bin.
Of those that don't race, the "well seasoned" opinion appears to be: AC hoses are not maintenance items. Replace when they start to leak, not on a schedule.
So that's what I'm going with. I ordered just the condenser and receiver/dryer.
(And I guess I owe AI an apology: that was its opinion from the start.
)'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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On my 944 (and 450SL) when converting to r134a, I changed any/all rubber hoses that were simple r&r jobs, but didn't change out any lines that required major disassembly to replace. At least on the 944, the system has held its charge 2 summers in a row now with no topping off needed yet. 
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dr bob
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Some rationalizations --
-- If the engine is out of a hose is otherwise easy to R&R, replacement or rebuild is the prudent option.
-- Local hose suppliers will rebuild your hose with new barrier hose plus your old ends and fittings.
-- Where there are long hardline assemblies with hose sections, the hose rebuild is a prudent option if you can get it out of the engine bay. Same rebuild effort needed as with other long hoses with short connectors. the same number of cuts and crimps.
-----
My 928 R-134a conversion included hose replacement, and with the engine in place the longer sections from the front apron to the evaporator were not coming out of the car without some serious engine/driveline gymnastics. Local AC shop offered to bring their portable crimping tool, so the rubber sections were replaced in situ. Still a lot of parts and other hoses removed, but they were done. So far, so good. In the words of the great bird-watcher and poultry chef John James Audubon, it's still pretty falcon cold in the cabin.
-- Well mineral oil saturated R12 hoses will do an OK but not perfect job of holding the refrigerant in. A conundrum is that PAG oil supplied in the compressors turns that to jelly. So, flush to remove at least the surface layers of old oil, or just use POE and avoid the jelly clogs? PAG means the oil embedded in the hose will make jelly and seal better, but you must get the oil surface oil out or it travels and clogs things.
-- If the engine is out of a hose is otherwise easy to R&R, replacement or rebuild is the prudent option.
-- Local hose suppliers will rebuild your hose with new barrier hose plus your old ends and fittings.
-- Where there are long hardline assemblies with hose sections, the hose rebuild is a prudent option if you can get it out of the engine bay. Same rebuild effort needed as with other long hoses with short connectors. the same number of cuts and crimps.
-----
My 928 R-134a conversion included hose replacement, and with the engine in place the longer sections from the front apron to the evaporator were not coming out of the car without some serious engine/driveline gymnastics. Local AC shop offered to bring their portable crimping tool, so the rubber sections were replaced in situ. Still a lot of parts and other hoses removed, but they were done. So far, so good. In the words of the great bird-watcher and poultry chef John James Audubon, it's still pretty falcon cold in the cabin.
-- Well mineral oil saturated R12 hoses will do an OK but not perfect job of holding the refrigerant in. A conundrum is that PAG oil supplied in the compressors turns that to jelly. So, flush to remove at least the surface layers of old oil, or just use POE and avoid the jelly clogs? PAG means the oil embedded in the hose will make jelly and seal better, but you must get the oil surface oil out or it travels and clogs things.
dr bob
1989 928 S4, black with cashmere/black inside
SoCal 928 Group Cofounder
928 Owner's Club Charter Member
Former Ex Bend Yacht Club Commodore Emeritus
Free Advice and Commentary. Use At Your Own Risk!
1989 928 S4, black with cashmere/black inside
SoCal 928 Group Cofounder
928 Owner's Club Charter Member
Former Ex Bend Yacht Club Commodore Emeritus
Free Advice and Commentary. Use At Your Own Risk!
Thankfully I don't have the R12 to R134a conversion issues. The car is a 1996, so was R134a from the get go.
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'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