"may someone explains me the "AC system" please ? for i can understand the meaning of this sentence :)"
As no one has yet been so kind as to answer Dann's question, I will clarify: AC is an acronym for "air conditioning", a concept that should actually be called "air cooling" as very few AC systems actually "condition" the air. We of the english-speaking world are sometimes over-fond of acronyms, which can get unintentionally hilarious when two well known groups or concepts adopt the same sets of initials (such as WWF being either the World Wrestling Foundation or the World Wildlife Fund.)