Generally, how much does a R134a retrofit/charge cost on a 1960's era Oldsmobile? I'm really getting an urge to get my AC working again, along with the heater, in preparation for the summer.
I'd be getting this done at a shop, because demons lie inside those hoses.

 

Really thinkin' the 134a conversion costs are going to be the least of your problems here, if the systems been laying around empty for years. You're probably looking at a compressor shaft seal, some hoses, and desicant for sure. You may consider leaving it an R-12 system, as 134a conversion generally requires flushing out much mineral oil as possible, going to synthetic oil. If the compressors getting swapped out, then not much of a deal, as where most of the oil's sitting anyway. Problem with 134a, is the factory R-12 condensor coil's a bit on the small side for the retro-fit, and may not do much cooling idling in traffic. Check around with a couple different shops, and see what they say.

 

I converted my 65 back to R12, it was expensive ($900) because you have to change the oil in everything because the 2 types of Freon use different oil. I changed it back because the my Air guy said the R134 works at higher pressures than R12 and that can cause several problems in an old system, he also told me the R12 cools better in a system made for R12. He was right the car now is like an ice box inside compared to when it had R134 in it.

 

If you convert to 134A, contact Classic Auto Air and see if they make a crossflow condenser, designed for 134A, for you model. I put one in my 72 Cutlass and it makes the 134A work much better. I get 2-25 degree air from the vents with little loss in traffic or at a stop. I live in south Florida. It is a direct bolt in for the Cutlass, exactly like the original. I also have one for my 70 Bonneville, that is different than the Cutlass, but same attachment as the original, so they may also make it for your Olds.

 

Well, if you think swapping to 134a is a good idea, on it's way out too. Thanks to the european union, say hello to R-1234yf. I've been in the refrigeration industry for year's, and definitely agree with some of the environmental changes made. Some of these changes yielded rather large impacts, but it's all political now. Recently going from R-22 to 410a residential/commercial, and now R-134a to 1234yf automotive, will do virtually zero environmentally. But cost of systems and servicing equipment will sky rocket. Our government dollars at work.

 

I had the conversion done on my 63 Starfire. New charge valves, dryer and refrigerant, and full system flush. I was very lucky that the original system had no leaks and held vacuum, usually other parts need to be replaced. total cost was about $400 at a good local shop. It works pretty well but if it has been sitting in the sun it takes awhile to cool down.