Refrigerant and oil are the only two residents allowed to exist in a refrigerant system. The refrigerant process — liquid to vapor to superheated vapor to superheated gas and back to liquid — will not work correctly if refrigerant and oil take on any newcomers in their neighborhood.
Meanwhile, nitrogen, oxygen, and water vapor are all trying to sneak in to the system. The evacuation process evicts these undesirable elements from the neighborhood. Today we will examine the terminology, procedures, and equipment used in the evacuation process.