I read somewhere that to do it correctly, you have to take the compressor out, disassemble it and clean it thoroughly because the oil in there is not compatble with the R-134 system. This makes the price much higher than just simply replacing nozzles and such. How much did you conversion cost and do you know if they took the compressor and cleaned it?
'92 ES300 is filled with R-12 - hard to find and pricey when you do find some. My '93 had the same problem a couple of years ago (no/little cold air), no A/C repair places would recharge with R-12 because it's illegal now (here in Canada, anyway). I didn't want to buy one of those R-12 recharge kits on ebay, so my only option was to convert from R-12 to R-134a refrigerant. I wasn't sure how well this would work, had heard (and read) some stories about this conversion, opinions were both good and bad. I just went ahead and had my ES converted - new refrigerant, receiver-drier, some new o-rings, and that was it. Not expensive (can't remember how much, but I was surprised it wasn't more $$), the shop gave me a warranty and 2 or 3 free visits to check that there were no leaks or problems. AC worked fine after conversion, back to normal. AC still works great, no problems at all.
If I had it to do over, I wouldn't mess with trying to find R-12 and recharge it. Just go to a good shop and convert it to R-134a.
tck...