AFTER: GEN III 2010. This is the scenario. Using my SMAN3 digital manifold. After 12+ min of vacuum it just hits past 29" vacuum about 6000 to 5000 microns, too long it should take about 3 min. I'v seen this many times before so I decide to preform a triple EVAC and nitrogen purge. I brake the vacuum with dry nitrogen and repeat vacuum. After 11:46 min it stop at 1444 microns, won't go any lower. Repeat brake vacuum with dry nitrogen, turn on vacuum, this time it takes 3:21 min to get to 1444 microns. Repeat 3ed time break vacuum and vacuum again, this time it takes 2:52 min to reach 1444, still to high, I continue to vacuum for 1 hour and still can only reach 1127 microns still to high. After turning off the vacuum and letting it stabilize 10 min it settles at 1500 microns. It has a new condenser, so you can leave it on the vacuum pump for 24 hours (not practical) or Flush the A/C system another $300 to $500 to the price and then recharge the system. This car looked like a salvage car by the way it was repaired. I noted the procedures I preformed and recharged it.
Remember this if you did not all ready know. The factory only wants to make it past warranty. GM only says to get to 700 microns. It should be 500 microns or less.
Here is a example. When I vacuum a new virgin A/C system it only take me 5min to 8 min to reach 500 microns. If I would have only have vacuum it to 29'' for 15min to 30min and recharged, this will end up being a come back ( sometimes it works some times not ) this is just one of the things water dose in a A/c system.Oh yea one more thing, the out side TEMP was 82F 10/17/11