Should the 'C' or 'F' be flashing on the control panel, the reason may be that the cooler is possibly set in the silent mode (depending on model, please consult your user guide for further information) The 'C' or 'F' light will flash every 2 seconds to indicate that silent mode is working.
Silent mode reduces the speed of the cooling fans and is the default or factory setting. To turn off the silent mode press and hold the light icon for 3 seconds, the 'C' or 'F' icon will then stay illuminated to indicate that silent mode is off.
Note; The control panel must be unlocked before any changes can be made to silent mode settings.