The invention discloses an air conditioner which mainly comprises a fan and an electromotor, wherein the electromotor is installed in the inner part of an auxiliary mounting system, and is connected with the fan through a driving belt; the bottom of the electromotor is also provided with an automatic regulating device with adjustable height; and the automatic regulating device is interconnected with the inner wall of the auxiliary mounting system. On the basis, the invention also discloses an method for installing the electromotor in the air conditioner, the problems that the descending of transmission efficiency and shaking at the like caused by the high slack possibility of the transmission belt in the prior art are solved, the aim of ensuring the transmission belt to be always at a tense state is realized, besides, the buffer effect for the shaking of the electromotor can be generated effectively.