You might investigate using Freeze 12. Supposedly closely approximates
the old Freon 12, both in it's performance and in it's resistance to
leaking down.

Sorry, I can't speak from experience now - but I have the same problem
as you, and I'm thinking more and more about going to Freeze 12.

John

On 1/21/2014 3:24 PM, mcneely4@cox.net wrote:
> My 1991 Volkswagen Vanagon GL Campmobile with factory air conditioning and a 2.1 liter engine (159k miles) loses refrigerant over the course of a summer.  It had it converted to R134a two springs ago.  It got all new fittings, the system was flushed, and new proper lubricant for R134 was added.  It cooled wonderfully well, but by summer's end it was not doing so, despite two shops claiming not  to be able to determine that it was leaking.  They reported that with a "leak down test" over 24 hours, it held proper pressure.
>
> So, next spring it needed recharging again, and again, "leak down test reveals no leak."  By summer's end, it was not cooling.  Recharging resulted in the thing cooling marvelously, air temperature from the plenum being around 48 F.  So, what do I do now?  I plan to use the camper this spring, summer, fall and will need air conditioning for some trips through the plains and Southwest.
>
> Help!
>
> David McNeely
> .
>