I, as I see many others on the forum, am playing around with aircon as summer is looming ever closer. I went to see if my somewhat recently acquired SDL (first summer under my ownership) would hold vacuum and I was very confused to see only one A/C fitting adapter. Before you ask, no, there's no blue sticker. That being said I just vacated/charged my other SDL and it has been converted and also has no sticker. The low pressure port (back by the intake) had a fitting adapter and a blue cap. The high pressure did not have a cap and was covered in gunk (carefully cleaned out as to mitigate any risk of contamination) so I assume it has been this way for some time.

So my question is: Is it safe to assume that the system has been converted from r12 to r134 because there is one fitting?

Thanks all!

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1986 190E 2.3-16 202k
1987 300SDL 384k
1987 300SDL 295k (1 of 1 Dark Green over Maroon)
1988 300TE 129k (sold to buy cossie)
1989 560SEL 424k
1990 560SEL 288k (sold)
1992 300E 131k

Yes. Whether it was done properly is an entirely different question. Put a high side fitting on and if the system isn't leaking, consider doing a flush and replacing the drier.

Laziness or a quick sale is why these car's don't get that other fitting.

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Allen Kroliczek
Oak Grove Autosport | Oak Grove Autosport
01 G500, 82 300TD, quite a few more.....

Great, thanks!

I'm only the third owner, prior to me it was owned by the same older lady for 29 years so I do not suspect any sort of malicious intent, however a flush and service will be in order. Thanks again!

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1986 190E 2.3-16 202k
1987 300SDL 384k
1987 300SDL 295k (1 of 1 Dark Green over Maroon)
1988 300TE 129k (sold to buy cossie)
1989 560SEL 424k
1990 560SEL 288k (sold)
1992 300E 131k

If like my 1985 300D, M-B used a strange size high-pressure R-12 fitting. I recall it has the same threads as the low-side fitting. I never found an R-134A adapter which fits it to give the modern high-side port. Perhaps not totally strange since I recently inadvertently bought a modern O-ring fitting on ebay with integral high-side R-134A port and it similarly had low-side threads which confused me. Had to buy another fitting.

When charging AC, I mainly use the low-side port anyway. Should be ~70 psig (both sides) after sitting overnight on a 70 F day and ~30 psig with compressor running on a 70 F day. Monitoring the high-side is mainly for trouble-shooting.

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1984 & 1985 CA 300D's
1964 & 65 Mopar's - Valiant, Dart, Newport
1996 & 2002 Chrysler minivans

If you intend on cracking the system open, either to flush or change the drier filter go ahead and get a new barrier hose set. Firstly, your current pre 134 hoses are at end of life, secondly the new hoses will be 134 barrier compliant which the r12 ones are not plus you get new Schrader valves in the new hose and should come with 134 fittings hi and low side.

Good luck

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Stable Mates:
1987 300TD 310K mi (Hans)
2008 Jeep Grand Cherokee OM642 165k mi (Benzrokee)