The Wal-mart and Advanced Auto parts sell  a kit, just for this.
I used one in a Jetta and it worked perfect.  The kit states
to just install and go.  I drained the compressor of the old
R12 oil, but in your case you will not have to do this.  I also
vacuumed down the system, twice.  This removes any
water in the system. I would recomend this.

                                              Eric

David Marshall wrote:

>I have a beautiful Vanagon Carat here that we are doing a TDI conversion
>into.  I have to admit that I am not an AC expert.  I know that the existing
>system has (or should have) R12.
>
>The 1998 TDI motor has a R134 compressor and we intend on using this
>compressor.  What do I have to change on the rest of the AC system in the
>Vanagon in order to use this R134 compressor and the R134 gas?
>
>Thanks in advance!
>
>David Marshall
>
>Fast Forward Automotive Inc.
>4356 Quesnel-Hixon Road
>Quesnel BC Canada  V2J 6Z3
>
>http://www.fastforward.ca    mailto:sales@fastforward.ca
>Phone: (250) 992 7775        FAX: (250) 992 1160
>
>- Vanagon Accessories and Engine Conversions
>- Vanagon, Transporter and Iltis Sales and Importation
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>
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