MOST SURELY evacuate!! im an A/C guy and I cant stress enough how non condensables (Moisture, Dye (yes even tracer dye in too much quantity can be detrimental), Oil (too much oil will make a system not cool well), Nitrogen, AIR). all will greatly impact (negatively) system performance..
you MAY be able to rent an A/C vacuum pump from an auto parts store. or perhaps a place like Sunbelt rentals. being its summer and moist outside the vacuum pump should run a minimum of an hour on a system like that... if it has been opened up long, id vacuum 2 hours.. your system will have a receiver / dryer. and that has a dessicant in it. which. takes a whilke to get the moisture out of.. moisture is opulled in the presence of a vacuum..
once vacuumed you should be able to punch at least a pound into the system. before you turn it on... punch that first can in Upside down. with the A/C OFF!!!.. this gets the most liquid in ..
now see what your standing pressure is... it should be up there at 60 or above once the refrigerant settles and evaporates... (in a system that size) unless its pretty cool outside...
after a few minutes, now start the van and turn on the A/C. you should see your gauge pressure drop on the low side. typically the low pressure switches are set low enough you can get the compressor to start.. or if they are using the factory system switches, it will kick in and out in and out..
** 25 PSI standing pressure may NOT bde enough to fire a low pressure switch thats been located on the high side. **. as mentioned you may need to find it and put a temporary jumper across the harness to get the system to run..
once you get the compressor running. put in the rest of the refrigerant as a gas.. meaning cans right-side up... the cans will get cold.. I typically have a pitcher of warm water to dip the can in to warm it up.. refrigerant will not flow from a frosty can.
hope this helps a little..
LOVE the red bus!! looks like the little brother to mine!!
I just evac'd and recharged the A/C on mine.. took out over 8 ounces of non-condensables... and its STILL a bit over-oiled.. but not bad