AC System Retrofits, Another View
Malcolm Davidow
from the Lone Star Chapter newsletter "das Bimmer Rundschreiben"
As an employee of one of the largest automotive temperature control manufacturers/distributors, I work with a number of the fine individuals who wrote the Society of Automotive Engineers' retrofit specifications. I am also a BMW CCA member and own a 1984 325iS. Previously I owned a retrofitted 1984 325e purchased new.
I would like to clarify some of the disinformation floating around about auto AC. Freon (i.e. R12, CFC12) is out of production as of 31 December 1995. (Stockpiles amounting to several million pounds of it remain, though).
Next and particularly important is the flushing procedure. Flushing with denatured alcohol, or any substance other than CFC12, is dangerous and disallowed under SAE, BMW, Sanden and Zexel specifications. BMW, Sanden and Zexel support the SAE flushing and retrofit specifications.
For BMW owners who choose to undertake an HFC134a (i.e. R134a, ICI Klea) retrofit with a Sanden or Zexel compressor, I highly recommend using a Sanden or Zexel compressor manufactured for use with HFC134a, not a compressor specified for CFC12 applications. Sanden and Zexel made design and material changes in order for these compressors to withstand the pressures of an HFC134a system and insure compatibility with the refrigerant, lubricants and elastomers. Both Sanden and Zexel charge their HFC134a compressors with PAG (poly alkaline glycol) lubricant. Use of an HFC134a-compatible makes unnecessary the step of draining the mineral lubricant. In addition, by using an HFC134a-compatible compressor, you will not be troubled with the decision between PAG and ester lubricants. You also have the option of installing a remanufactured HFC134a-compatible compressor. I know that these remanufactured units are available from Sanden, but I am not aware of one from Zexel. Industry-wide fleet test results indicate an HFC134a charge of 80 to 85 percent of the specified CFC12 charge yields higher system performance.
It is noted elsewhere that "An R12 compressor that is functioning properly does not have to be replaced with one made especially for R134a". If the compressor is a Behr-Robert Bosch rotary vane compressor, applied to nearly every BMW model from the early 1980's through 1991, you must replace the compressor when retrofitting to HFC134a. The Behr-Robert Bosch compressor contains an elastomer that disintegrates when coming in contact with HFC134a, PAG and ester lubricants.
If the compressor is functioning properly, with the current supply of CFC12 at current pricing, there is no reason to undertake a retrofit. The car makers, trade associations, SAE and EPA advise against a retrofit unless 1) CFC stocks are depleted; 2) CFC 12 becomes prohibitively expensive, or 3) you have experienced a major system failure.