Abstract: An improved evaporative cooler contains a first pump for supplying cooling liquid to the evaporative pads and a second pump for draining liquid in the sump pan through a drain/overflow pipe. Both pumps are coupled to an electronic control mechanism which activates the first pump for a first predetermined period of time within each successive second predetermined period of time (e.g. the first 2.5 minutes of every successive 10 minute period). The control mechanism causes the second pump to drain the sump pan through the drain/overflow pipe for a third predetermined period of time following the first occurence of the first predetermined period of time (e.g. for 5.0 minutes after the first 2.5 minute wetting cycle). This draining process occurs only once each time the evaporative cooler is turned on. The drain/overflow pipe has an upper end coupled to the outlet of the second pump and also has an aperture in the wall thereof through which excess liquid in the sump pump will flow and be discharged.