the pressures you are reporting make me think bad fan clutch, and contaminated system.
vacuum holding for 30 minutes how? do you have a micron gauge to see pressure change?
the rubber hoses, and leaky compressor in mobile a/c systems are NOT designed to have extended vacuum done on them. nitrogen flush, and quick high cfm vacuum, is needed in automotive applications.

the 30psi low is fine, but the 250 high is out of range... at idle. most likely, you have air in the system from the vacuum, and changing cans during the charge.
if it were me, I'd dump it all, and change the dryer, and purge everything with Nitro, then leak test under pressure with a splash of R22, then evacuate that and charge from a 30LB cylinder of 12... but I've got all that stuff.

put a jumper on the pressure switch leads, so the aux fans stick on, and bump the idle up to 1500 or so, and tell us what you have.

__________________
John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 560SL convertible
1987 190D 2.5-5SPEED!!!

1987 300TD
2005 Dodge Sprinter 2500 158"WB
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!