A/C oil recharge

[Das Delfin]

Hey so my buddy is an HVAC tech and last week we learned that my car's original R12 A/C system holds a vacuum. We pulled it for an hour and then let it sit for two hours and the gauges didn't move one bit. Which is great.

We discovered that at one point in time someone had put an R134a adapter on the low side schrader fitting. So the car had that in it at one point. But this would have been multiple years ago as the car's compressor belt was missing when I bought it three years ago. My buddy has a 609 and is able to get R12 old stock so we're going to go that route rather than converting. I'm thinking about just taking the online class to get my own.

What I'm wondering is how much oil charge should I put in the car? I don't know how much is in the car now. Would I have to evacuate the system to clear it all out? Or would the vacuum pump do that somehow? From what I've been reading I don't really have to add much oil at all, and at most maybe 2oz.

Any advice or tips would be appreciated! I'm learning about A/C systems as we go and this forum and youtube/the internet has helped a ton. Thanks!

[TobyB]

...someone had put an R134a adapter on the low side schrader fitting....What I'm wondering is how much oil charge should I put in the car? I don't know how much is in the car now.

...and what kind...

From what I've read/watched, when you have no idea how much of what kind you have,
it's time to flush the thing multiple times, blow it out, and start all over.

Which always gave me a headache.

The easiest advice I got was "don't worry about it". Idea being, the oil only leaks out
when you take components off, and if you haven't lost any (or much) you don't need
to add any. That assumes, of course, that the right amount was in there to begin with.

The 134 fitting would make me think it MIGHT have been converted to 134,
and I dunno how to test for that.

t

[jeffnhiscars]

The oil has to be compatible with the refrigerant and r12 uses mineral oil. Not 100% but I think ester can also be used with it but you may need to flush the system (which you should do anyway). If your friend is an ac tech he should know this.

As far as how much, it depends if the system is new or whether you have just replaced certain items.

Standard is 10 cc per or hose and more for an evaporator, Connor or compressor. I just don't recall exactly and don't want to give you poor info. That's the idea though.

And you'd best know what was in there before you start adding anything. System death can result from a mistake....and pulling a vac shouldn't change the amount of oil left since it doesn't vaporize at vacuum

[Das Delfin]

The r134a deal looks like it was a quick ditch effort to restore A/C. The original R12 compressor is on the car and the original R12 sticker is still on the car. I doubt a conversion has been done since any shop would have replaced the sticker and everything else looks original.

That being said, the system is empty of refrigerant at the moment. I haven't replaced anything. I was geared up to convert to r134... until the car held a vacuum on its original system.

I've also read that "don't worry about it" is the best way to go. There's no reason for oil to leak out, right?

I don't think PAG oil has been added because; 1. What we're talking about here; 2. It seems like more effort than a previous owner would have wanted to do based on the rest of the car, and; 3. None of the seals have decomposed.

I've read that there should be an oil drain plug on the compressor and some way to fill it at the top so you can drain it and compare that to how much is spec. Although since the system is closed atm it shouldn't be that far off, taking into consideration there will be some oil throughout the system. But I'll get under the car and take a look

Thanks for the info, guys.

[jeffnhiscars]

Ive had converted systems run extremely cold with all the original hardware so which compressor you have doesn't really tell us anything. There are 2 deals with using stock compressors...1 is that they are not dsigned for the right pressure range for optimum r134 performance although there are lots of cases where it did just fine (including my example above).

More importantly is that BMW issued a bulletin for which production dates have seals that will tolerate r134. If yours is one of those the condition of your seals would not be a sign of what refrigerant you have.

The adaptor fittings are highly suggestive of a change. Not 100% but no other logical reason for it to be there.

If you have the old drier with some residual oil in it you might take it to an ac shop and ask if they can tell if it's pag or mineral oil. If you can access the exapnsion valve that "should" have been changed as part of a conversion but then you already know it's a hack job so that may not tell you anything.

Best practice with all these unknowns would be to thoroughly flush the system and use ester which plays well with both r12 and r134....oh...my new compressor held 150cc of pag and if you change the condenser or evaporator add 20cc for each.

The only real risk I see in which way you go is oil/refrigerant compatibility. Everything else is luck.

[Das Delfin]

Mine is an early 1987 which as I learned a few weeks ago is just before they switched to the dual compatibility seals. So if it had r134a in it, it must not have had it for long. I've read about r134a molecules being smaller than r12 and they can seep through non-barrier hoses (like what's on my car) which would explain why the system is empty. I wouldn't be surprised if the A/C has been inoperative for a decade. What's weird is the original R12-only seals are still good.

There is an EPA law which states if a conversion has been done, a replacement sticker must be placed over the original R12 sticker. So if any kind of retrofit had been done by a shop, it would have this sticker, plus valve adapters both high and low. Right now only the low has been swapped and there is no EPA-regulated sticker. I figure a $5 adapter plus a $30 autozone r134a kit = a cheap attempt at A/C.

You're right, there is a certain amount of luck but mostly I am trying to make an educated guess without taking it apart!

I'll try bringing my old dryer to a shop and see what they say

[jeffnhiscars]

Production dates and models with compressors from the factory that ARE NOT r134 compatible:

E30
318i 7/85-8/85
325e, 325i, 325iC 7/87-10/88
325iX, M3 all

Bosch compressors that are also NOT r134 compatible:

64 52 1 377 940
941
943
944
946
947
64 52 1 385 416
930
64 52 1 386 411

[Das Delfin]

Interesting! Mine is a 6/87. So my compressor would be good to go for a conversion! (assuming it's original) It ALSO would have been able to handle the higher pressure of r134a which means it's likely still good after all these years

I don't think it's a bosch but I'll double check

[jeffnhiscars]

r134 works best at higher pressures which an r134 specific compressor is designed to generate. If you run it in a compressor designed for r12, you run at r12 pressures so you just don't get the same cooling efficiency. As long as the seals survive the compressor doesn't care which refrigerate rant you run.

You definitely want to have the matching expansion valve and they didn't all come with Bosch compressors so I'd say the production dates are more telling as long as it's the original