Vacuum pumps are part of one of the final processes in the repair process. After you’ve diagnosed and repaired any leaks 
or Ac Vacuum Pump various other issues in the system it’s time to recharge. Before recharging you really want to make sure the machine is free of any unwanted gasses, air, or water. If these were to stay in the machine, it could turn the oil it runs on into sludge and leave behind damaging impurities.
The draw on vacuum pressure pump is usually broken down into its “CFM,” or Cubic Feet per Minute. To estimate what your CFM needs, consider the tonnage of the systems you work on. Take the square root of that number and you’ll obtain the approximate CFM you need to have to utilize that system. Typical home systems need 4-5 CFM, while commercial and rooftop systems generally require as much as 6-8 CFM.