The reason that Montag wants Faber to do these things (and a variety of other things) is so that the Mechanical Hound will not be able to pick up his (Montag's) scent. He is hoping that he will be able to escape and that the authorities will not find out that Faber has been helping him.
The Mechanical Hound works by scent and it has been given Montag's old flame thrower to smell. Montag wants Faber to do various things to destroy Montag's scent. By turning on the air conditioning, he will recirculate the air and Montag's scent will be diluted. By turning on the sprinklers, he will wash Montag's scent off the sidewalk. By doing these things and others like them, Faber might be able to trick the Hound and prevent it from picking up Montag's scent. This is why Montag wants Faber to do these things.