Vacuum pumps are part of one of the final procedures in the repair process. After you’ve diagnosed and repaired any leaks or additional issues in the Ac Vacuum Pump system it’s time to recharge. Before recharging you need to make sure the machine is free from any undesirable gasses, air, or water. If we were holding to stay in the system, it could turn the essential oil it runs on into sludge and leave behind damaging impurities.
The draw on a vacuum pump is usually broken down into its “CFM,” or Cubic Feet each and every minute. To estimate what your CFM requirements, look at the tonnage of the systems you focus on. Take the square root of that quantity and you’ll get the approximate CFM you need to have to utilize that system. Typical 
residential systems need 4-5 CFM, while commercial and rooftop systems generally need just as much as 6-8 CFM.