A method for checking functions of fans includes starting a normal operation mode, evaluating a fan monitoring signal depending on the fans' speeds, and starting a dynamic fan checking routine. If the monitoring signal is smaller than a lock threshold value, normal operation proceeds. If the monitoring signal is bigger than the lock threshold value, a multiple-fan checking routine is started. During each fan test the corresponding fan is activated for a predetermined time period, while the other fans are deactivated during the time period, and the monitoring signal is compared with the lock threshold value and a disconnecting threshold value. If the monitoring signal is bigger than the lock threshold value, the corresponding fan is locked and an error is detected. If the monitoring signal is smaller than the disconnecting threshold value, the corresponding fan is disconnected and an error is detected.