Important Information:
It has been known for systems to be Re-Charged using Hydrocarbon based refrigerants e.g. propane or methane mixtures. This means you could be driving around with a potentially lethal mix of gases in your system which in the event of an accident/collision could lead to the risk of an explosion.
If you suspect your system may have been recharged with such a mixture, why not have Sub Zero run a check for you.