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For your health, peace of mind and cost savings, get an EPA certification/permit to purchase R12 and find out what specific lubricant is required. (Really, you can download the open book test for it and it's not expensive). At least not nearly as expensive as
having to replace all the parts you're going to destroy by filling your R12 system with
Freeze 12 or R134a.
You can do it and it will run for awhile but the internal component/seals won't last too long. When you mix/run a combination of R12 with 134A the high side pressure can go through the roof (boom). The PAG (mineral)oil in your R12 system is not compatible with ester oil required for a 134A. You need to really really "flush" a system out to remove the old residual oils before moving on towards a freon coversion.
I'm not sure where you located but here in the U.S. one needs a minimum of a Type I card (EPA certification/permit) to purchase and legally use R12. Get a hold of some R12 and reload your system or do some search on coverting to 134A.
You might look around your local area and see if you can dig up some old stock of R12. My best garage sale find ever was 2 totally full 30 lb bottles of R12....gave'em their full asking price of $10 for both...they were thrilled to get the money.