bureau13

That's the same as on my 924. I would have sworn this was some sort of aftermarket or at least dealer-installed afterthought, but the user manual has pictures of it.

924RACR

Question to the crowd... I too have the earlier of the earlier (but not the really old aftermarket system) on my '82 931. Did the quick and dirty conversion to 134, in that I didn't drain the compressor before switching over. It worked, but not awesome; the greenhouse in the summer (even up here in MI) keeps it from being awesome. In fact, it can only really ever just take the edge off the heat, driving home from work in the afternoon.

Having just fixed a bunch of other crap on my car, I'd love to get the AC back up and running better. I have a few options, as I see it, would love to hear the thoughts from those who've really plumbed the depths of these systems.

In order of increasing cost:
1: top off the 134 as best I can. Does the rule about bubbles in the sight glass work for 134 too? All the discussion here seems to be on 12.
2. Finish empyting the system (car has sat for some years, expect my charge is low now though I haven't actually checked). remove and drain the compressor (how exactly? Just turn it over and let it drain from the ports?), and reassemble and fill fresh with 134 and compressor oil. This could help if the old R12-compatible oil is in there making a mess of things.
3. Get a new style compressor that's designed to work with 134 (Sanden was a name I remember hearing about, at least a while ago), and swap that in with a fresh fill.

Thoughts?

bureau13

A couple things: Did you add any oil when you converted, and if so, what kind? R-134a is not compatible with the mineral oil originally used in R-12 systems. I would not run the compressor that way for fear of burning it out. Also, PAG oil, the oil used in new R-134a systems, does not play nice with mineral oil, so unless you've flushed ALL of it out, you need to use POE oil, which will work with the new refrigerant and won't turn into jelly when mixed with mineral oil.

Also, when you converted, did you replace all your o-rings with the newer green ones? If you don't do that, the new refrigerant will likely leak out. It may anyway, slowly, through any soft lines in the system, but the occasional top-off is no big deal, IMO.

What I would do, personally, since you've already been running with R-134a sort of, is flush out the system (especially if you put any PAG oil in there), replace all the o-rings if you haven't already (and the expansion valve because you might as well at this point) and then fill it with an appropriate amount of R-134a and POE oil. I don't see any reason to change out the compressor if it's working. As far as I know, while there are newer, more efficient compressors, there were not actual design changes for the new refrigerant. My 928 is using the same compressor for R-134a as it did for R-12, and it works fine.

Perry 951

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Pretty much everything he said is spot on for a 12 to 134A conversion. The oil incompatibility is the biggest issue and leads to metal wear in the compressor and sends it into orifices in the system.

924RACR

Thanks for the reply... yes, I did swap the o-rings, it held up pretty well, but didn't empty the old oil out. What would you recommend for a flush, should I just drain and rinse with brake cleaner or what?

I guess we'll see if the compressor still works, but it used to. Haven't run it at all in some years due to other car issues.

Question on the 134 fill I didn't see answered, I assume the no bubbles in sight glass works just as for R12?

tempest411

Site glass observations don't seem to work for R134a. At least that's what I've read in an AC training manual I have...