how about r-500 refrigerant
 

A friend of mine has a 30 pound drum of r-500. The r-12 has leaked out of my '79 300SD. I know that r-500 has a higher head pressure and is very similar to r-12, but would it cool as well as it did with the r-12 originally? I don't need to hear as to why I should keep r-12. The car holds 2.2 pounds of r-12, then how much r-500 would it take? What kind of pressure readings would I want to see? Haven't gone into details with him yet as to what might have to be retrofitted. Would anything have to be changed to run r-500?
Thanks
David

^

If you don't want to hear anything about why not to use R500 then the only thing that I have to offer is that you answered your own question when you indicated that it will cause high head pressure.

If you want to significantly decrease compressor life, then just raise the high side pressure by using a refrigerant with incorrect pressure charecteristics.

Good luck,