Disclosed are an air conditioner, a method for controlling outdoor units thereof, and a central control system having the same. A mode conversion unit such as a boot loader is provided to perform a mode conversion between a driving control mode and an upgrade mode in a software manner, without requiring a user's visit to the site. This may allow an outdoor unit control program to be remotely upgraded. In the present disclosure, the air conditioner may return to a previous mode or previous program in the occurrence of an error on an upgrade signal or upgrade program.