Before air conditioning became a complex pressurized system, there was the Swamp Cooler that hung on the top of the passengers door. This system was very simple and quite effective. It wasn't the most attractive thing to have that bulky unit hanging on your door and it does interfere with your vision out the right side.
The swamp cooler or evaporative cooler functioned by collecting air in the front and passing it through a saturated drum that was constructed of wire mesh and filled with fiber material that would suspend water. The mesh drum is rotated through the water in the bottom of the unit with a pull cord in order to saturate the fiber as it dried. The outlet for this would be set to enter through the top of your door window.
These coolers bring a pretty good premium now. You can usually find a few to choose from on internet auction sites.