Refrigeration and air conditioning

A German engineer who charges a system has to choose a verb, and the verb decides which noun is the object. Kältemittel einfüllen makes the refrigerant the object: something goes into something. Die Anlage befüllen turns the sentence round, and the prefix be- is what does it. The system becomes the accusative object, and the refrigerant, if it is mentioned at all, follows with mit: die Anlage mit Kältemittel befüllen. English does both jobs with one verb, to fill or to charge, and lets the preposition sort it out. German builds the same pair across the language: Kisten auf den Wagen laden but den Wagen beladen, Farbe auf die Wand sprühen but die Wand besprühen. The be- verb also tends to mean the whole container: die Anlage ist befüllt reports a system that is charged, not one that has had some refrigerant put into it.