I am placing a 12 inch AUX fan to help with the R134 convertion need help on the best way to wire it up so it will turn on automaticly when AC is turnd on :)

http://elcaminocentral.com/articles/electfan/auxfan.gif

the clutch wire am i taping in the the ac + wire?

the clutch wire am i taping in the the ac + wire?

You want the fan to turn on whenever the clutch cycles, so tap in to the clutch + wire at the compresser or pressure cycling switch.

Robert wouldn't it be a good idea to wire the aux fan to come on with the AC and not only when the clutch cycles on? My thinking is that if the high side pressure gets too high (hot day, idling in traffic) and the clutch cyles off then it would be useful to have the aux fan blow air across the condenser core even when the AC clutch is disengaged.

The way I suggested to wire is the way most vehicles with condenser fans from the factory are wired. Also, this is how I wire vehicles I put aftermarket a/c systems in. Wiring it the way you suggest isn't a bad idea either, I guess it really depends on preference, but realize too that once the compresser cycles off the pressure in the system gradually drops as well, so high pressure really isn't an issue with compresser off. Also, keep in mind on a really hot day in traffic, the compresser is probably not going to cycle out often (unless you have the blower set on low, or install a high pressure cutout switch) but continue running until evaporator temp/pressure drops.
As I said, it really is preference, you could also wire it to run off of a switch too.

http://elcaminocentral.com/articles/electfan/auxfan.gif
the pic works fine ac blows 40