The Air Conditioner at first comes off as a cold and uncaring figure who prefers that the other appliances forget about the Master. He also seems to have a very short temper. In truth, his cold indifference seems to be a facade of what he really feels, as shown when the other appliances argue about the Master's reason for leaving them. He clearly dislikes the fact that the Master never played with him when the Master could not reach his dials as a child. He is jealous of the other appliances because they can move freely about while he is stuck to the windowsill (or the wall from his point of view); but by the near end of the film, when the Master returns and repairs him, finally showing him kindness, the Air Conditioner is seen happy for the first time, smiling and being driven to tears by his Master's actions.
When the appliances are saddened by the Master's long absence, the Air Conditioner tells them that they are abandoned forever with him and the Master is never returning. But when they refuse to believe him, he begins to stubbornly rebuke them, and when they mention why the reason he is so unfaithful, which because of the lack of attention he received from the Master, he begins to angrily yell at them that it was the Master's own fault for not being able to reach him. He soon becomes so outraged that he overheats and explodes. (He may have also tried to free himself from the wall).
At first, it appears he was right after the appliances learn the cottage is being sold, but when the Master returns to the cottage to pick up his old appliances, he finds the broken Air Conditioner and repairs him. As soon as the Master leaves, the Air Conditioner is finally seen smiling, with tears of joy in his eyes, realizing he was wrong.