Originally Posted by LarryBible

I'm not willing to make that bet if it's my car. The consequences of being wrong are too big.

The only way to KNOW what refrigerant is present is with a Refrigerant Identifier. Any auto a/c shop will have one and can check it in five minutes.

If the car were mine, I would buy a filter/drier and maybe an expansion valve along with o-rings. I would then break the entire system down, thoroughly flush, put everything back together with the filter/drier going on last and not until I was ready with the vac pump. I woul already have removed the adapter fittings and added the correct amount of oil. I would then evacuate and charge with R12.

Even if you could use your 134 gauges, you should not do this. You should not let your gauge sets be contaminated with dissimilar refrigerants and oils. R12 gauges are very inexpensive. Much cheaper than a 134 gauge set.