I have to replace my a/c hoses (the expensive one broke) and I was thinking of converting to 134.  I call an a/c compressor shop in Irving, Tx to see what really needed to be done as many have said almost nothing other than the fittings and o-rings.  He said I have to completely flush the system (ugh) and replace the seals inside my A6 compressor.  Then he said that it still won't cool very well with the old style condenser.  So now I see no benefit to changing over.  4 lbs of R12 is about $160.  A new condenser and compressor rebuild would be more.

Gary, my '72 was converted to R134 before I aquired it.  It cools but not too well when the temp goes much above 90 degrees or so.  I read somewhere that on Corvettes of this vintage you have to add an electric cooling fan on the condenser to make it cool right, however that is not an option for me as I am one of those NCRS nuts.  You didn't mention replacing the dryer and I would think it would need to be replaced or rebulit also. 

I wouldn't do r12 again unless you are absolutely certain there are no leaks.  Its too expensive to let leak out.  I suggest just using Envirosafe ES-12a drop-in replacement for r-12 from www.autorefrigerants.com.  Some people swear by Freeze12.  I just charged up a friends car with Freeze12 and he's been reasonably happy with it for the last month.  Neither require flushing or changing the compressor or replacing seals, but Envirosafe suggests that if your system needs an oil charge at the same time, to add Ester oil rather than PAG or mineral.  Both drop-ins work better than r134 and the es-12a comes pretty close to r12 performance.

The reason they need to do so much work to convert to r134 is that it won't pick up and circulate the heavy mineral oil that was used in the r12 system.  They have to flush out all the old mineral oil and replace it with PAG oil.  As to the seals, supposedly there's no real evidence that the seals used in old r12 systems are incompatible, but shops like to replace them for good measure (and to make money).  Given the level of work compared to performance and the fact you've got decent drop-in alternatives, its not worth converting.

Actually there is evidence.  The 143 molecule is smaller that the 12 molecule.  It passes through a 12 o-ring due to the composition of the rubber.   BUT once in use for several years, the oils and other chemicals will seal these seals and they will then hold 134 with no problem.  So the only issue is if you used new R-12 seals.  But almost all seals you can buy now will hold R-134a, so there usually is no problem.

Before heading west to last year's C3VR gathering in Carson City, NV I took "The Beast" in to have the A/C system checked (as well as a few other things).  Had to replace the condenser so I was asked if I wanted to stay with the R-12 or convert to R-134.  They made a good case for converting so that was the route I took (I'm disappointed that they didn't offer any other alternatives-which I'm sure they knew about). 

I have converted quite a few cars through the years, and I mayslf, have been satisfied with the results. Is it the perfect fix, by all means no. I just finished converting my '70 convertible to 134a, it still gets warm inside, but I believe that has to do with the black soft top and 100 deg. temps. I converted my wofes '71 coupe last year, and it is VERY comfortable to drive in the heat. It is NOT like the newer cars we own, bu tI can live with the difference. MikeMc712008-09-09 02:53:08

Ken (kstyer) is correct about the smaller molecules of the R134A. You really have to chang out the "O" rings to the proper composition material. The system must be flushed to remove the old oil. A new drier would be used. The system really needs to be evacuated before metering in the refrigerant. Another thing that I would recommend is to repace the VIR with this: https://www.zip-products.com/Zip/productr.asp?pf_id=AH-463&gift=False&0=dept This has the proper "O" rings etc.

This might be of some interest to you: http://www.aa1car.com/library/retrofit.htm

[QUOTE=pdupler]I wouldn't do r12 again unless you are absolutely certain there are no leaks.  Its too expensive to let leak out.  I suggest just using Envirosafe ES-12a drop-in replacement for r-12 from www.autorefrigerants.com.  Some people swear by Freeze12.  I just charged up a friends car with Freeze12 and he's been reasonably happy with it for the last month.  Neither require flushing or changing the compressor or replacing seals, but Envirosafe suggests that if your system needs an oil charge at the same time, to add Ester oil rather than PAG or mineral.  Both drop-ins work better than r134 and the es-12a comes pretty close to r12 performance.

The reason they need to do so much work to convert to r134 is that it won't pick up and circulate the heavy mineral oil that was used in the r12 system.  They have to flush out all the old mineral oil and replace it with PAG oil.  As to the seals, supposedly there's no real evidence that the seals used in old r12 systems are incompatible, but shops like to replace them for good measure (and to make money).  Given the level of work compared to performance and the fact you've got decent drop-in alternatives, its not worth converting.


[/QUOTE]

Sounds like this is the way to go.  I'll do some more internet research on it but I like that it is totally compatible and works better than R134.  Thanks for all the info.  This place is great.

[QUOTE=corvette440hp]Ken (kstyer) is correct about the smaller molecules of the R134A. You really have to chang out the "O" rings to the proper composition material. [/QUOTE]

Now that y'all mention it, I do vaguely recall reading something like that.  I also remember another quote about o-rings compatibility, but after searching for half an hour, I can't find it now.  Oh well, sounds like our friend has decided not to do the r134 conversion anyway.  Good move I think.  Eventually, for originality sake, we've got to "unconvert" Roger's 72 and its probably gonna be a chore.