A problem with any such mixture is not just leakage, but preferential leakage of the smaller molecular weight component. So the mixture changes as it leaks, and should be evacuated any time refrigerant is needed. All A/C hose in the R-134A era is barrier type for a reason, and R-134A will diffuse through the older non-barrier type hoses. Combined with leakage through micro-cracks in the hoses, that means needing to add refrigerant on a regular basis.

Personally, I would not trust any of these "drop-in" replacements to provide sufficient mineral oil carrying capacity to protect the compressor. The secret to making R-134A work right is hose replacement, and upgrading the condenser (Nostalgic Air has a perfect 16 x 22 parallel flow unit - if replacing hoses and fittings), and using POE or PAG oil.

Keith Hughes '86 Westy Tiico (Marvin) - in Phoenix AZ

------------------------------ Date:    Wed, 22 Jan 2014 13:32:46 -0600 From:    Dave Mcneely <mcneely4@COX.NET> Subject: Re: Air Conditioning help My apology, and you are correct.  Freeze 12 is 80%R134a and 20% R142b.  It is not a hydrocarbon.  Is this true?  Freeze 12 was developed so that R12 systems could be recharged without changing the lubricant.  The 142b carries the lubricant, but the 134b actually does the cooling. You find all kinds of stuff, some valid, some not, on the internet. Of course, mixing the 134a with another refrigerant would not alter the molecular size of the 134a, so if it is leaking because it is smaller than the pore size of the hoses, or from breaches that are too small for R12, so what? I think I'll take the advice that said try harder to find the leak(s), fix them if found, and recharge the system.  If it is still leaking after another round, I may give up on the AC, and just swelter.  I don't use AC at home much, even when it is brutal, unless someone is sick. mcneely