Yes there is a lot more to know.
First, if you have a vanagon, you do not have R134 unless it has already been converted. you have R12 and they cannot be mixed (either physically or legally, and niether can their oils). If you are thinkng of using one of those walmart Interdynamics conversion kits, my advice would be don't.  the process is much more involved than it seems from the kit.  If you are going to do a 134a conversion right you need to evacuate the system, flush it, change the seals, change the receiver/dryer, add PAG oil, vaccum,  then charge (and I may have missed some stuff as I writing quickly -- Like there is a rule on high pressure cut off switches, but I dunno if it is applicable to vanagons).  If you need more feedback on those kits go to aircondition.com in the questions board and look at all the posts from people who bought the kit, got cold air for a short time, then destroyed their A/C system  THEN posted questions about how to do it.  That site is also a great place to learn and get ques!
tions answered. GO TO THAT SITE BEFORE DOING ANYTHING!!!!
BTW: if you are trying to convert just so you can get the refrigerant and so to do the job yourself, I recommend you go to epatest.com and spend 18.00, take a test and get certified so you can buy R12 (or Freeze 12 which I think ken at vanagain likes and is a lot cheapre than R12.)  Off the cuff, and without trying it, I do not believe our vehicles are good candidates for 134 conversions anyway -- r12 and r134 systems ARE different in many ways not the least of which is the higher pressures of 134 (and smaller molecules leading to leaks) and the need for a larger (preferably crossflow) condensor.  That's my opinion.  Charlie.