Hello, new a/c compressors have a shelf life of about 18 months. The shaft
seal will shrink up and leak afterwards.If your vanagon is pre 86, you dont
have a low pressure cutoff switch.This prevents the a/c from turning on
where the pressures get too low. You see, the oil circulates with  the
refrigerant,and will leave the compressor and not return if you operate the
a/c with low freon. You have probably had low freon for awhile and didnt
know it.First thing to do, know matter which way you go, is to remove the
compressor and drain the oil to see if you have any left. Normal oil is 8
oz. If you got 4 , you are probably ok. Under  load, the compressor will
probably make noise if you recharge w/oilless compressor.Next, look up the
# for southeast air in texas. They can sell you  a low pressure cut off
switch to prevent this from happening again. With the switch, your system
will not operate (like all other vehicles) when freon is low.It is screwed
into the high pressure access port,then connected in series to your
compressor.The EPA licence/test is avaliable on Ebay for 7 dollars.