Normally the water tank is in the bottom, and a fountain pump is used to pump the water up to a drip hose at the top of the cooler pad.
They work the best when pulling fresh air in through an open window, and having a second open window on the opposite end of the vehicle. A direct style swamp cooler works by replacing the warmer air with cooler air, rather cooling the warmer air like an A/C does, so the open window on the far end is needed for maximum efficiency. This makes it much quicker & more effective, while using very little power. Basically just whatever power the fan uses, because the water pump uses practically nothing.
If the water pump is circulating the water too fast, sometimes it doesn’t get the chance to cool the water as much as it can if there is less circulation. I have a valve on mine to regulate the water pressure, and it can definitely make quite a bit of difference. You may need to readjust due to humidity, elevation or ???.
If necessary, it’s also possible to cheat with just a damp T-shirt in front of a fan, or you can wear it too. Damp pajamas or onesies with a fan aimed at you can cool you down in a hurry too, and they’ll be dry before morning.
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