This could happen because the Smart AC Control is not positioned correctly. Or because the Smart AC Control is not sending the right commands to your AC.
Make sure that the Smart AC Control is in the direct line of sight of your AC unit and that it is not too far away from the AC.
If your Smart AC Control is positioned correctly, then go to the respective room settings in Settings > Rooms & Devices. Try resetting the installation process by choosing Restart AC Setup.
In Standard Mode, if your AC reacts to the ON command on tado° (i.e. if it beeps), but it does not switch on, please contact our Technical Support.