First it is the system oil that is incompatible with the different refrigerants. In order to do the conversion properly you must depressure the system, remove the compressor and accumulator and drain them, flush the hoses with a cooling system flush, reassemble (preferably with a new accumulator) with compatible o-rings at every connection and vacuum test. Once it holds the vacuum for 30 minutes, or so, refill the system with the required quantity of oil being careful not to ingest any air along with it, and recharge with refrigerant that is compatible with the oil used.
There are "snake oils" in both the refrigerant oil and refrigerants that claim to be compatible with each other so that you may avoid the conversion process. Some of this stuff a propane derivative that is extremely flammable. This stuff appears to be another CFC that the EPA has deemed "safe" but, beware, there are some of these that are propane derivatives which are extremely flammable. The MSDS is here: http://www.technicalchemical.com/msds/6030.pdf . As for the oils, some are marketed as having the ability to mix together and allow refrigerants to be co-mingled. Use at your own risk!
Bottom line, R-134 is what the EPA and Feds have deemed "safe" to use so ultimately the conversion is necessary. The trick is to get a good vacuum evacuation after the conversion, NOT pull air in with the refrigerant oil, and recharge properly and fully. R-134 runs at ~10% higher pressures than R-12 to supply the same cooling so that, in itself, may cause some component failures (hoses, mostly). Also, the expansion valve or orifice tube must be in good condition as that is where the "refrigeration" takes place.
The new vehicles these days that use R-134 will "freeze you out" so it is not the refrigerant's fault but the design of the old systems that we are trying to convert. It is a compromise, at best.
As an aside, there is/was nothing any more toxic or harmful in R-12 than ANY of the replacement refrigerants we struggle with today. The problem was that DuPont's patent was expiring on R-12 so they developed a "safer" replacement and patented it to enrich DuPont! Lobbyist money will buy LOTS of legislation these days!
Mark in Texas
Sid,
Here is a source on a product called Freeze-12 listed at Amazon. Anyone used this stuff?
http://www.amazon.com/Freeze-12-Refrigerant-R-12-Replacement-Can/dp/B002EQKP2Q
Chip
Houston
--- In diesel_mercedes@yahoogroups.com, "Chip" <czulli@...> wrote:
>
>
>
> Sid,
>
> My German mechanic that uses nothing but dealer Benz parts has a stock of it, not sure where he got it. I am not sure what he wants to charge me to change over my system. These two things might be closely related!
>
> I understand that there is an R12 that can still be bought that has some modification but works, not sure of the name.
>
> I also hear R12 is cheap and plentiful in Mexico but that's a bit far for you and a bit dangerous for me.
>
> Chip
> Houston
>
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