Vacuum is necessary for refrigerator and AC before charge Gas. we vacuum with vacuum Pump or with any old Compressor. By Vacuum Wind expires from our unit. we need Vacuum Pump or Old Compressor and Line Gauge for Vacuum any unit. When you do vacuum your unit should be off. One Line Attach with Suction pipe and Gauge and Second Line Attach with pin Valve pipe and Gauge. Open the gauge and On vacuum pump now vacuum is start. we should do vacuum 20-25 Minutes.