The vacuum pump is used to evacuate the refrigeration system to remove air and moisture from the refrigeration system. When installing and servicing the air-conditioning refrigeration system, a certain amount of air will enter the refrigeration system. The air contains a certain amount of water vapor, which will block the expansion valve of the refrigeration system, increase the condensation pressure, and cause corrosion of system components. Therefore, after the refrigeration system is overhauled, the refrigeration system should be evacuated before the refrigerant is added. Whether the vacuum is thorough or not will affect the normal operation of the system. Evacuation does not directly draw water out of the system, but allows the system to generate a vacuum to lower the boiling point of the water, so that the water boils at a lower temperature before being drawn out of the system in the form of steam.