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Vacuum Pumps: what to look for. #1: vacuum pump rated at 15 to 25 microns. There is a vacuum pump rated at 0.1 micron but its not for automotive use and it starts at $1200 for a 1.5 CFM pump. For automotive use you should at least have a 6 CFM if you do any retrofit from R12 to R134 use a 6 CFM. If you any van, truck or Hybird with dual evaporators with all that extra a/c lines going to the rear you need a 6CFM. #2: Good ones range from $350 to $450 Always test your vacuum pumps with a micron gauge often vary often!. For A/C it should easily go below 500 microns and for refrigeration below 200 microns. changing your oil will make a difference. I leave mine some times on jobs running 24 hours. Some time on a clean dry system it take less the 15min to go below 500 microns on a hot day, and some times it takes way over 1 hour to even reach 500 microns. As you can see have a few vacuum pumps and 3 more not shown here are on jobs running over night. When they no longer pull a vacuum under 500 microns for A/C its time to send then in for repair or buy a new one.