R12 - R134a conversion - A/C compressor - BMW M5 Forum and M6 Forums

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Old 5th June 2013, 22:20   #1
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R12 - R134a conversion - A/C compressor

Hi all!

So I am in the process of upgrading to an R134a A/C system on my '91, and my car has a Bosch compressor (PN 64 52 1 385 416) that needs to be replaced. It is one of a couple of compressor part numbers that are unfortunately not compatible with R134a. There are some other threads in this forum that do a good job archiving this. The attached image is the list of part numbers that will NOT work with R134a, taken from the BMW service bulletin about retrofitting R134a (from 1996!). Hopefully this can be of some help as well!

I am posting because I am trying to figure out where I could get a remanufactured Seiko/Seiki compressor (PN 64 52 8 363 550) for less than the dealer's quote of $750. Part of that quote involves a ~$100 bracket that "may or may not be necessary." This statement agrees with what I have found on these and other forums about Seiko/Bosch compressors and which engines they fit on with/without brackets. Bav Auto has a reman compressor for $800 but does not match the part number, and there is no mention of a bracket.

Apart from doing a junk yard search on car-part.com, does anyone have any positive experiences here? The labor for the conversion is already going to be pretty high, so if I can avoid any part cost markup, that would be a pretty big help. But at the same time, I want to do it right. I am thinking about the longevity of this fine hand-built beast, and don't want to half-*** anything. You just don't do that to an M5 :-)

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Old 14th June 2013, 10:14   #2
Alan Archer
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I've always used a very knowledgeable A/C guy for the cars in my family.
Every visit he would show me A/C units, cars and compressors in various states of undress.

He's retired now, but we spoke a few times about the swap from R12 to R134 a.
He used to do conversions for customers who would bring him a "kit" consisting of a bunch
Of o-rings to replace and not much else.

We both understood the potential for o-ring system seals to react to the change & he listed
The merits of replacing the receiver/dryer unit when upgrading.
But I don't ever recall him having compressor issues.

Infact he told me that on some very old motors he simply took a deep breath & gassed them up with 134.

If I were in your shoes I would be tempted to do the same.
The worse senario is that your system leaks and you have to then strip/fix it, in which case you're back where you are now.

But worth a shot I think.


///M5 the only substitute for capacity is even greater capacity...

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