I have heard so many stories of bad outcomes with 134a conversions (even by 'pros'). I'm not saying it can't work, just that doing it right is often more complicated than advertised.
It would seem that many outfits are trading on a false public perception that has created something of a 'conversion industry'. Large amounts of money are changing hands, often for the wrong reasons.
Let's face it. There is more money to be made from expensive conversions, and the r12 they reclaim from your system has a market value, so they win twice. If the converted system melts down in a year or two, not their problem...
The cost/benefit analysis is out of whack when expensive retrofitting is done to save $80 on refrigerant. Sure, it will leak over time, but will a topoff every, say, 3-4 years break the bank?
I think part of the perception problem dates back to when the price for r12 was dramatically higher for a time, which may have been partly driven by speculators. Anyways, demand is predictibly down now. 10 years has elapsed, and there are fewer vehicles is operation that use r12. Many of the remainder have been converted. Appliance and industial users have converted.
Fed taxes are around $9 per pound now, and will climb $.45 every year forever, but hopefully the recycled supply will meet the smaller demand, and keep inflation fairly low for years to come, or at least until a better cooling technology is invented...
I used to buy 2 pounds of r12 for a dollar on sale in the '80s. Can you imagine?
1986 300E 5-Speed 240k mi.