A control device and methods for controlling an air conditioner are provided. The control device includes: an interface configured to receive measurement information indicating a detected indoor temperature; and a controller configured to, after initiating an air conditioning operation according to a set temperature which is inputted by a user, determine occurrence of an event according to a pre-defined criterion based on a relationship between the indoor temperature of the received measurement information and the set temperature with time, and, in response to the event occurring, change the set temperature.