This instructable will show you how I converted a 240 volt rooftop Evaporative air conditioner to a Mobile unit run on my DIY 12 volt solar setup.
My setup supports the 2 most important things in the house.
The 12 volt Beer fridge and the Air Conditioner.
Without either of these the summers here would be unbearable.
There is also something quite satisfying about sitting in a cool house sipping icy cold beer on a stinking hot day knowing the sun has done all the cooling.

Step 1: The Beginning.

First you need to obtain an old evap air cooler.
I bought mine on ebay for around $200. Winter is the cheapest time to buy one.
A trip to the local rubbish tip netted me an old BBQ on a stand with wheels at one end. I left the rusted out BBQ there and took the stand home.
A wooden pallet went with me.
The Air Cooler then had all the electrics, the huge 240 volt motor (unfortunately not permanent magnet) and the 240 volt pump unceremoniously ripped out (taking up space in my shed now if you want them).
It was then attached to the aforementioned pallet which was screwed to the top of the BBQ stand.
Now it's ready for step 2.

Step 2: The Pump.

After a look around I found that ebay had the cheapest 12 volt pumps that looked capable of doing the job of running enough water up to the top of the cooler panels.
I chose a 360 gallon per hour one purely on cost and Amps used (it uses about 2 amps).
It proved to be not quite powerful enough so I stopped the water flow to one of the panels so there was an adequate amount going to each of the other three ( I covered the now unused panel with plastic).
If your 12 volt system can support a bigger pump then buy a bigger pump.
About 500 gph would be perfect.
I have to be careful with every amp my panels produce.

Step 3: The Fan.

The hole that the old fan came from is 20 inches in diameter.
The Fan I chose for the unit is a single speed 16" after market car Radiator Fan.
It pumps lots of air and only draws 7 Amps.
I had to make an adapter to attach the fan to.
I used Masonite.
I cut a 20" circle and cut a 15" hole in the center of that.
I drilled a few holes and attached the fan with cable ties.
I mounted the wire cover off an old fan over the top of the fan to keep the Frogs out of the fan.
I should have mentioned earlier that the Air cooler has become a Frog habitat. Seven were living in it at last count. Any port in a drought eh.

Step 4: The Bendy Shiny Stuff.

After a bit of a play with the kids 3 meters of the bendy shiny stuff, ducting to us grownups, was attached to the bottom of the cooler with duct tape.
I made a square wooden adapter for the house end and mounted it in an open window.
I bought a ducting vent attachment and screwed that to the wooden adapter.
The ducting was attached to that and the cooler was ready to be wired up.

Step 5: Wiring.

I built a switch box out of an old pc power supply case, added 2 automotive on/off switches and 2x10 amp fuses and ran the wires from the pump and fan through that to the load outlet on my solar controller .
Sounds simple because it was.

Step 6: Water.

Our water pressure is too high to connect the float valve in the cooler directly through a hose so I trickle water into a 10 liter container and it flows from that to the float valve and into the cooler reservoir as required.
Any excess flow into the 10 liter container runs through an overflow pipe to a bucket.

Edited 30/11/2012.
We have moved into the village of Bethungra where the water pressure is much lower.
This has enabled me to connect the cooler to the town water mains and has simplified things immensely. No more filling containers to gravity feed into the cooler and much better water flow over the pads.
Still have Frogs living in it though. I have no idea how they get in there but they seem to love it.