Are older R12 a/c systems better sealed than newer 134 units?

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Two examples I'm working with. 1) 2001 Escort not used since 2017. A/C not working and gauges show zero pressure. Did the 15 minutes on a vacuum pump followed by 15 minutes rest. Vacuum held steady so no obvious leaks. Assume seals just shrunk from inactivity and will be ok after some use. 2) 1988 motorhome not used since 2011. Never imagined the A/C would work after sitting that long, but a few days ago I hit the A/C button and the compressor engaged, noisily for a little bit, but the air blew cold. Far as I can tell it's still on R12. Do these old systems hold a charge better?
 
I'm going on 25 years on the R134a system on my Club Sport; it's never lost any R134a.
 
When R134 came on the scene, a lot of people were installing the "R12 to R134 conversion kits" sold at nearly any parts store. As previously mentioned, the R134 molecules are smaller and the refrigerant would literally seep through the hose linings on a R12 system.
 
From what we're being told, this may be one of the benefits of the switch to R1234yf, as it is going back to a larger molecule again. Sadly, it costs like 5 times what R134a does.
 
What everyone else said, the R134a molecules are smaller than R12 molecules, hence more seepage

In fact, some A/C leak detection dyes have larger molecules than the 134a itself, so it's possible to have a leak that the dye can't detect
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It may not help you, but I have a 97 Ranger and the compressor leaked at the shaft seal. I got a kit online and resealed it for fairly cheap. Not that tough of a job.
 
At the compressor outlet, 134a runs hotter and that tends to harden the o rings in the line from the compressor to the condenser. Those are a common place to leak in both systems but it may be worse with 134a.
 
R134 uses better hoses and o rings. But is a smaller molecule at higher pressure.

I have three r-12 systems, one leaks and the others are tight.

They said it was important to run your ac in r-12 systems so the oil could coat the lines. I do that.
 
Originally Posted by john_pifer
I dunno about being sealed better, but those old R12 systems sure did blow colder, faster!


I agree. I think R-12 leaked more, unless you converted to R134 and left the R12 hoses---that leaked a lot. Newer vehicles designed for R134 have different hoses that contain the smaller molecules that the R12 hoses could not. In my experience most R134 systems will run on factory fill until a part fails with no leakage, whereas most R12 systems needed a top off every few years.
 
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