Make sure you have water to the unit, the water pump is on and the fan is working. No water=no cooling.

Evaporative coolers are only for dry climate conditions or deserts. They cannot cool as much as central air or air conditioners which have compressors and refrigerant. The mechanics are simple requiring a water float valve, pump, spider (water distribution), aspen wood pads, blower, belt, motor, and switch. The unit must have a water supply to replenish the system due to evaporation. Your system may have a float valve which you need to adjust to shut off when the water pan is full. Floats can be adjusted by loosening the pivot screw and moving the float up and down to adjust the turn off level or by turning the float to extend or retract the length changing the water shutoff position. You do not want the water to be so high it flows out the over flow tube but the water should cover pump base. Plug in the unit and turn the switch to pump if you have that option on your unit. This will engage the pump to force water from the pan up to the spider to saturate the pads with water. After a few minutes turn the switch from pump to low or high cool. New aspen pads will have an distinct smell which will go away after a few days of usage. If you do not have a pump setting turn the switch to low or high cool which will blow warm air at first then start to cool down. You may also have a fan setting which will blow outside air without any additional cooling if the outside air is humid. Occasional maintenance is to make sure the pump is pumping water and the filter basket is clean and all the spiders are working with water flowing freely. You can use a flexible wire to force it in a spider tube to clean it if it is clogged. You may want to change the water after a month to keep the system cleaner from slime and calcium. At the end of the season disconnect the water supply and drain the water pan blowing out the water line if the winter is below freezing. Replace the pads if they have calcium build up or dry. Flush the water pan out and clean the Add some oil to the pillow blocks which are the bearings at each end for the blower. Check the belt and pulley for excessive wear. Cover the unit with canvas to prevent cold air from coming in during the winter. Next summer season all you have to do is uncover the unit and hook up the water supply.