Basically because it's a violation of Federal law.

http://www.epa.gov/Ozone/snap/refrigerants/hc12alng.html

Some folks think the intent is to force people to have their old R-12
captured instead of venting it to the atmosphere. It almost reads like
they're acknowledging an unintentional  loophole after the fact. I'm
thinking most people that are converting are doing so because they lost
their R-12 charge in the first place and they don't want to pay the price
for it now.

At any rate, the only legal retrofit from R-12 is R134a, but they didn't
regulate retrofits from R-134a, hence the loophole and the three-part
progression.

Compliance with the law as a practical matter is of course a personal
choice, but there you have it.

Cya,
Robert

----- Original Message -----
From: "Zeitgeist" <gruengeist@GMAIL.COM>
To: <vanagon@GERRY.VANAGON.COM>
Sent: Thursday, August 03, 2006 12:16 PM
Subject: Re: My R134a experience

> If you're going to use Duracool, why go to all that bother and switch to
> 134a first?  Duracool is made up of butane, isobutane and propane.  I'd
> just
> cut out the branded middleman and run straight propane and isobutane --
> much
> cheaper, and it cools quite well.  YMMV
>
> On 8/3/06, John Rodgers <inua@charter.net> wrote:
>>
>> I have had this dilema myself, as I am getting ready to rebuild my
>> system using a stock compressor. I have decided to stick with the R12,
>> or at least one of the R12 look-alikes - Duracool or some other. To use
>> a refigerant that is not R12 nor R134a, you must first have your rig
>> converted to R134a, then change it to the new R12 substitute. You must
>> go through the R134a stage to get to a Duracool system or other like
>> setup. And the system must be thoroughly flushed between changes.
>>
>> I think I saw somewhere that if you go for a duracool or like
>> refrigerant, the goal is to wind up with a R134a valve and a R12 valve.
>> So you would have at the start 2 - R12 valves, next you would have two
>> R134a valves, then when you are done, and install th Duracool, you are
>> supposed wind up with both the R134a and the R12 valves. Not sure for
>> why though.
>>
>>
>> Casey
> Olympia, WA
> Biodiesel: "I drive in a persistent vegetative state"
> '87 300TD intercooler #22 (216k)
> '84 300D (214k)
> Gashuffer:
> '89 Vanagon Wolfsburg Edition (187K)
> http://users.zhonka.net/zeitgeist/Misc/IMG_0171.JPG