[Texas944]

any pump should pump down to atleast 24 inches of mercury within the first half hour. If you sucked it down for 24 hours with no sign of leakage, then that should have been more than enough. Believe it or not, i have had more success with quicker suck down times than longer ones. When i got my first vacuum pump i would let it evacuate a system for hours. I have found that with shorter evacuation times i get colder A/C. When i recently did my blazer, i only sucked it down for an hour - the oven meat gauge i have stuck in the vent shows 38 degrees on high. When you say 45 inches of mercury on the low side - what psi is that - you should have between 25 and 35 psi there. No more than 225 on the high side. As for the couplings - when they come off they dont usually let any air in, but you dont normally dissconnect them until after you have charged it either.