I have a similar setup on my gas 16v and I'd love to have the belt run as per the diagram with a double sided belt. If you find one please post it. I will be seing if my parts guy can get one too. I didn't know the compressor could turn either way. Thanks!
As far as my A/C guy knows all that is inside a sanden is a pison and valve. He told me it was exactly like the old detroits that could run backwards. He also said that he found most of this because when he fills a new one and oil comes out you cannot spin it the other way and turn the output into suction. It will just continue to puke out the output no matter which way the pulley spins. I am not an A/C tech so I know this only as second hand, but the guy I deal with is pretty good with this stuff so I am going to believe him until I ruin a compressor
From my understanding of the compressor design there are spring loaded ball valves in the suction and discharge of each piston (someone please correct me if I'm wrong) which results in the ability to rotate the compressor either direction and still have it operate correctly.
I also found an interesting post,
http://www.thesamba.com/vw/forum/viewtopic.php?t=367871&start=0,over on The Samba which discusses retrofitting a system from R-12 to R-134A. The post talks about higher discharge pressure, more wear on internal compressor components, and the requirement to switch to PAG oil from mineral oil for compressor lubrication.
Yes, changing over isn't that difficult - you need a kit (usually comes with o-ring, oil and some fittings). This needs to be added to the R-12 fittings so you can fill it properly. Change the compressor oil, change the air dryer (in a MK2 it small round thing connected to the condenser behind bumper) and you're set.
I think I'm just going to use R-12 for my Jetta. I just got my EPA Section 609 cert (for motor vehicle a/c systems) so I can now legally buy R-12 or R-134a for that matter. I've got a line on a 30 Gal Cyl here in the Puget Sound area that I might be able to get. If I can get it then I'll have enough R-12 for about 10 systems
All I'll need to do is have an A/C shop do a flush, draw a vacuum on the system and verify no leaks, add the compressor oil, then have them draw a vacuum on the system again. I'm going to try and find a place where I can rent a vacuum pump so that I can draw the vacuum the second time myself.
If anyone is interested in getting there EPA cert (for those of you in the US) I got mine from
http://www.epatest.com. The test for the cert is 'open book' so I downloaded there study guide/practice test/ exam program and had it done in a matter of a couple of hours.