In Chapter 7, of Catcher in the Rye, Holden goes into Ackley's room. Holden has just had a fight with Stradlater over the essay that Holden wrote for him. Stradlater tore up the essay; Holden was very upset about this given the essay was about his deceased brother's baseball mitt. Stradlater began hitting Holden and eventually pinned him to the ground only promising to let Holden up if he kept his mouth shut (Holden had repeatedly called him a moron). After the fight, Holden decides to go into Ackley's room because he had certainly heard the fight and was awake. Holden also wanted to see what Ackley was doing given that Ackley had very bad "personal habits".
Holden is not received very well by Ackley, initially. Ackley was awake when Holden entered the room after the fight with Stradlater. The fight had woken him up. Holden refuses to tell Ackley what the fight was about and then asks him if he can sleep in Ely's (Ackley's roommate) bed. Ackley refuses to say it is okay for Holden to sleep in Ely bed, given the bed is not his to give. After repeated inquires about the fight, Holden tells Ackley that the fight was about him and that Holden was "defending his ...honor". Holden tells Ackely that he is kidding and lies down in Ely's bed. After Ackley falls asleep, Holden decides to leave.
All in all, Ackley seems to be concerned about why Holden is in his room. Regardless, Ackley does not truly seem to care if Holden stays or leaves. He, in fact, seems to careless about Holden. Therefore, he receives Holden with indifference.