Hello, What is the best means of "sniffing" and characterizing the freon or refrigerant in an AC system? My 81 MB has the original receiver/dryer, compressor, etc. When I cycle it, it blows barely cold, though the compressor does engage. I do not think it cycles though. My concern is that there is a "quick connect" fitting on the low side of the system. I have all records for the car, but I do not have any record of a recharge. The air blew plenty cold all last year. Still, if the PO did something stupid, like topped R12 with R134, I want to make it right. If it was a matter of simplicity to use the quick connect to do R12 (which may be illegal, right?), then I want to still make it right. I have R12 and can top that, but I want to be definite. Is there a way to DIY this, or do I need to take it to a shop? Say someone did something stupid like top off with Freeze-12 or similar, how can I be sure that I account for this too? Now, two other quick questions: -the car is 28 years old and all original. Does it make sense to evacuate the system and do an "oil change" anyway? -if I want to top it off, can I use my R134a gauges for R12? I know the fittings are correct to do this. Is there a set of best practices to purge either out prior to switching to the other refrigerant? Thanks!