Freon is a Dupont trade name for the refrigerant family it manufactures. The compound that used to be used in almost all auto air conditioners, as well as in some regrigerators and window a/c units, was R-12. R-12 is a CFC, which SOME researchers CLAIMED depleted the ozone layer. So the sale in the US of R-12 was phased out, and it became comically-expensive in its final months of use.
It was replaced by R-134a, which works ALMOST as well but which will leak out of an R-12-engineered refrigeration loop. So an R-12 loop needs new hoses, valves and seals in order to pump R-134a. It also uses a different type of lubricating oil, which means that all the old R-12 oil has to be cleaned out as well. In most cases, it's simpler to just replace R-12 components with those made for 134a.
There are other refrigerants trade-named Freon which are NOT R-12. For instance, R-22 Freon is what's used in central air conditioning systems and heat pumps and in larger vehicles like big motorcoaches (buses). R-22 is an HFC and doesn't tend to screw up the ozone layer as SOME scientists CLAIMED R-12 did.
In actuality, there may have been another reason for the demise of R-12 - one that had nothing to do with science and everything to do with Dupont's profit picture. You see, Dupont's patent on R-12 was set to expire just about the time that the so-called ozone hole at the South Pole began to be noticed by SOME scientists. Once Dupont's patent expired, ANYONE with the proper equipment could manufacture R-12 and Dupont would lose its monopoly. Dupont, which has a very heavy presence in TENNESSEE, was not a happy camper.
So Dupont voiced its concerns to TENNESSEE Senator ALGORE with the SUGGESTION that perhaps another, patented refrigerant could be substituted in autos IF the federal gubmint were to force R-12 into extinction - just coincidentally at the time Dupont's patent on it expired.
And, lo and behold, that is precisely what happened.
Now, there are some "drop-in" replacements for R-12 for use in older cars - I'm not sure how well they work - but there's no point in using them in newer post-'94 cars because R134a is pretty cheap and readily available. And, of course, DuPont gets paid every time you buy a can of th' stuff.
And THAT - is the REST of the story.
Michael