The present disclosure relates to a control device for controlling an air conditioner, AC. The control device comprises IR transmission means for emitting control signals to an AC; a microphone for measuring audio acknowledgement signals produced by the AC; and electronic control and evaluation means configured to determine whether sounds measured with the microphone include an audio acknowledgement signal produced by the AC, and being configured to perform a power state determination procedure to determine a power state of the AC. The power state determination comprises: sending a first control signal which is not an on/off control signal and determining whether an audio acknowledgment signal of the AC is subsequently measured, and judging whether the AC is in an off-state depending on whether an audio acknowledgment signal is measured subsequent to the sending of the first control signal. Furthermore a corresponding method for controlling an AC is disclosed.