How do you clean the outside of a swamp cooler?

You can use Lime-away to remove mineral deposits from the outside of the swamp cooler (also called an evaporative cooler), but I think you may be asking about the mineral deposits that are on the cooler pads. New pads should be installed every year. Go to your local home improvement center to get the pads and ask for some brief instructions. It's a simple process and isn't very expensive.