What is the ruling on showering more than once during the daytime in Ramadan, or sitting for extended periods near an air conditioner that emits humidity?

It is permissible to pour water over the head and there is no harm in it. The Messenger of Allah (peace be upon him) used to do so while fasting due to heat or thirst. Ibn 'Amr also used to wet his garment while fasting to alleviate the severity of heat or thirst. The moisture does not affect the fast because it does not reach the stomach.