I'm not sure how it will be on your ship but on all the Carnival ships I have been on you can adjust the air by turning a knob at the vent. There was not a thermostat just the knob adjustment. Hope this helps.
Sorry about the short answer before, I was answering from my iPhone which has a tiny keyboard.
There is not a thermostat but you can adjust the amount of cold air flowing from the vent. If you like it cold for sleeping you can get the temp pretty low.