Ventilation of drainage system for frame engine evaporative cooler

An evaporative cooler for cooling air includes a cooling housing having an air inlet and an air outlet and an evaporation media, located within the cooling housing intermediate the air inlet and the air outlet for air flow there through and for receiving water to permit evaporation of at least some water. The evaporative cooler includes a drain pan located within the cooling housing and below the evaporation media to catch water which has not evaporated and falling from the evaporation media and a sump located within the cooling housing and below the drain pan for collecting water for use in supplying water to the evaporation media. The evaporative cooler includes a pipe connecting the drain pan to the sump for water movement from the drain pan to the sump and an air vent located within the cooling housing and connected to the pipe, the air vent being open to air within the cooling housing and above the drain pan to permit release of air from within the pipe.