BMW: a/c compressor, highschool physics, rubber sections

Question
87 325 e  , my a/c compressor froze the other day, i'd like to know if i can replace the r-12 compressor with a 134a compressor and have the system evacuated. thank you

Answer
Eddie,
 I have heard you can, and I have heard you cannot do this.  To answer this question correctly I would need to be an A/C expert.  This question is not BMW specific, and would pertain to any vehicle with A/C.  
 Since you are changing the compressor to a R134a compressor, that eliminates the largest problem.  The next issue would be the two lines that connect to the compressor.  These lines have rubber sections, and that's where leaks can form.  Stepping back to highschool physics, you will remember that atoms placed together form a molecule.  Some molecules are larger or smaller than others.  R12 is considerably larger that R134a, so if you have hoses that are designed to keep R12 in, they may still allow R134 to escape through the pores of the rubber (Constant small leak).  
 Some people say that the oil charge that is introduced with the refridgerant coats the inside of the rubber hoses, and stops the molecules from escaping.  This is debated heavily by some.

 So If I were you I would look on this site for an expert at A/C, and ask him what he thought.  But on the other hand, I changed my system, introduced new oil and refridgerant, and I have had no issues.

 Good luck,
 Josh