Chevy metro AC

I have a 1998 chevy metro that has a bad leak in the AC system. I was told that while the leak could be fixed the system could no longer be charged because of the type of refrigerant it needs. Is there any truth to this? If so, is it possible to put in a different AC unit?

The only thing that comes to mind is that the shop detected contanminated refridgerant and do not want it in their recovery machine.

Geo Metro, I have put many compressors on them,hard to find leaks on,they use R134A,have no other idea.Only hold .9lbs for a charge.

Try a different shop.