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This depends on a lot. I would go with Envirosafe ES-12 since R12 is getting hard to find uncontaminated. But if he wants to charge your system with R134A then you should swap out the compressor with one made for R134A because the older R12 compressor doesn't handle R134A very well!
The older R-4 type tends to blow when the temps go above 100*F because it cannot handle the higher head pressures of R134A that are required to generate the cold air your looking for. If you install a compressor made for R134A from someone like Mapco, for instance, then your more likely to get the performance your looking for using R134A.
If you stay with the R-4, then I would go with ES-12 and about 6 ounces of compressor oil and call it good. I can hang meat in my car on hot days with ES-12.
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