Where to get AC recharged

[sxk122]

I have a can.... comes 'free' with purchase of the cheater hose, lol

[MC70]

I don't know squat about AC systems; one of those things I just never got around to learning. Is there a year cutoff that they went from one refrigerant to another? Any easy way to tell?

I span all three generations in the cars:

'90, AC equipped but doesn't work
'94, AC seems to work fine
'96, AC blew colder before I had NTB check it (they instead purged and refilled it but told me it was different refrigerant :/ )