Its a coleman evaporative air cooler. It works by drawing water up from a holding
tank and spraying inside the unit where the fan blows the cooler air back inside
the cab.
Ive got one in my old Bedford Motorhome.
Like most water based air cooller's it works best in a dry climate rather than a humid/coastal area.
Ive got some stuff on how it works if you want I guess I could scan it and post it on my gallery etc.
In the mean time here is what dad had posted on his oldholden site
Coleman Evaporative Air Conditioner
THE "Coleman Model ,,6254" Evaporative Air Conditioner here is how it work's small dependable, low amperage pump, mounted on a 6 gallon water tank, delivers water on demand ,through the supply tubing up to a distributor tube in the cooling unit on the roof of the vechile, it flows into flat high speed revolving slinger .
the spinning slinger impinges the water against a circular fence located inside on the housing top and directly above the incoming air chamber.
This action vaporises the water into a fine mist .The fan ,located in the venturi above the ceiling louvers, draws outside air in through holes in the housing air passes through this fine mist were it gives up some of its heat to the mist as the mist evaporates. The air is drawn on through the filter pad where it is cleaned and free droplets of water is removed. It then passes down through the lovers in the ceiling where the cool clean air is delivered into the vechile. Excess water, that does not evaporate in the cooling process, falls to the sump at the bottom of the roof unit and flows through a screen ,through the outlet and into the return line, the water flows through the return line and by gravity returns to the tank and then is ready to be recirculated, It's an excellent unit, will operate on high and low fan, also as an exhaust fan.
http://gallery.oldholden.com/d/107007-2/Coleman+Evaperrator+Cooler.JPGcheers
ian