Vacuum pumps are Ac Vacuum Pump component of one of the final procedures in the repair procedure. After you’ve diagnosed and repaired any leaks or other issues in the machine it’s time to recharge. Before recharging you want 
to make sure the machine is free of any undesired gasses, air, or drinking water. If they were to stay in the system, it could turn the oil it runs on into sludge and keep behind damaging impurities.
The draw on a vacuum pump is usually divided into its “CFM,” or Cubic Feet per Minute. To estimate what your CFM needs, consider the tonnage of the systems you focus on. Take the square root of that quantity and you’ll get the approximate CFM you must have to work with that system. Typical home systems need 4-5 CFM, while industrial and rooftop systems generally require as much as 6-8 CFM.