Mastercool evaporative coolers come in a number of different styles, but the common element of a Mastercool is the pads, which are thick paper pads that can last several seasons if they are kept clean. Evaporative cooler use is limited to areas that have low humidity levels and high summer temperatures. These parts of the country also have hard water with lots of dissolved solids that collect on the pads, reducing their efficiency. Keeping the pads and the cooler free of the deposits is the biggest chore in cleaning a Mastercool cooler.
Turn off the cooler and unplug it. Let others know you are cleaning the cooler so they don't inadvertently plug it back in and run it. The coolers have many moving parts that can be dangerous when cleaning them.
Hook the hose up to a spigot and put on the sprayer nozzle. Heavily encrusted pads may require a pressure washer to completely clean the pads, although you can do an effective job using the hose at its highest setting with the narrowest spray setting to increase the water pressure.
Take the frame or frames off the cooler to access the pads. The pads may be hard to remove since the sit so tightly inside the frames. Most Mastercool coolers use metal holding bars to anchor the pads in the frames. Remove the bars and take out the pads. If they stick, use a screwdriver to loose the edges of the pads until you have enough of a grip to lift them out. Note the top of the pad, which probably has a thick fabric piece on top, which better distributes the water flowing out of the cooler's spider.
Turn on the water and set the nozzle to a spray setting. Prop the pads against something vertical and begin spraying the pads to knock the loose dirt and deposits off the outside of the pad. Turn the pads over and do the same with the other side.
Inspect the fins on the frames. If they have any mineral deposits on them, use the hose and sprayer to clean the deposits off. Deposits can form on these fins and impede airflow coming into the cooler. Do not use sharp metal objects to clean the fins because the paint can flake off, creating rust on the cooler frames.
Look inside of the cooler. If sediments have deposited on the bottom of the cooler, remove the overflow pipe and drain the water, using your hand to make sure that all the solids mix with the water so they flow out the drain. Finish cleaning the pan by turning the hose down to low and flushing out any remaining dirt or salt deposits.
Put the pads back in the frame, verifying that you put the top of the pad at the top of the frame and reinstall in the cooler. Put the overflow pipe back in and refill the cooler.
If the water in your area is excessively hard, prompting frequent cooler cleaning, consider installing a bleed-off line or a sump pump to reduce the build-up of deposits on the pads.