Air coolers are designed to work best in an environment with a steady supply of cool air. If you have the option, it is always better to have a window on your cooler for ventilation and light. However, if you do not have a window, using an air cooler in a room without ventilation can work as long as the cooler is running constantly and has good airflow. The cooler will be able to cool down your room faster than if there was no air-cooling system present at all.