'93 B2600 Freon R-12 or R-134?

My '93 B2600 has R-134 fittings, but the engine bay label has R-12 on it as the freon. Has anyone found this and the facts, R-12 or R-134? Is there a known clue, such as stamped on the compression?
With '93 being the change over year, could they have used the soon to be regular R-134 lines, having run short on R-12 lines (fittings are different)?
Any solution to this is appreciated in advance.

No, the 1993 were all R-12 from the factory. What happened on yours is that someone converted it to R134a and didn't put the required-by-regulation sticker on the hood underside.I wouldn't have recommended converting to R134a, but since that was done in the past, keep it R134a. Several in Florida, Texas, and Nevada have reported on MazdaTrucking that their conversions have worked well in their trucks (mine is still R-12 in Arizona). The compressor would be the same. The R134a service fittings are the clue.

By the way, I have enough tools and fittings that I could theoretically use R134a in mine without changing the service valves, but that would wreak havoc for anyone else in the future.

Two things: 1. NEVER add any sealer, or any refrigerant that contains sealer, sealant, or conditioner. UV leak detection dye is OK to add though. 2. If your system is low on refrigerant, then YOU HAVE A LEAK. There is really no such thing like "just needs a recharge". By regulations, not legal to add refrigerant to a known leaking system, except in the process of finding a leak.

Thanks Cusser, I got the truck running poorly on a half dead ecu (cylinders 1 and 3). It has set three years (since it was tagged last and died before I got it). So you figure it has the right oil in it for R-134, with the R-134 fittings screwed onto the fittings in the lines? Hate that, I have a tub of R-12 I bought in the '80's when it hirt a dollar a 15 oz. can.

Yes, I do "assume" that if the fittings are Acme for R134a, then the oil is also for R134a. If mine, I could confirm with a few drops of refrigeration oil obtained from the system (instrument at work, less than 5 minutes).

If I draw a good vacumn on the system, the R-134 oil will be drawn out also? Then I can replace valve stems in the original fittings and charge with R-12 oil charge and then R-12, thus be running at lower pressures? I ask this from anyone who knows more than I remember from A/C school in the early seventies.

Oil is not volatile, will NOT come out with vacuum. But what you are asking is do-able. You'd need to take things apart and flush condenser, evaporator, lines with solvent. Do not flush compressor with solvent, you'd flush several times with R-12 type refrigeration oil, turning the compressor through several revolutions each time. Use new drier. Replace all the O-rings with new.

Okay, sound like it would be simpler and maybe as cheap to just use R-134, thanks Cusser