an apparatus for cooling an enclosure uses cold ambient air drawn into the enclosure by an intake blower through a filter and an intake valve . an exhaust blower simultaneously draws air from inside the enclosure through an exhaust valve and a filter before exhausting the air . the intake and exhaust blowers are switched on and the intake and exhaust valves are opened when the ambient air is cooler than the enclosure and the enclosure requires cooling to remain within an acceptable temperature range . condensation on the valves is eliminated by making the valve bodies from an insulative material and by attaching insulation to the valves . two element valves are disclosed which trap a pocket of air in the valve for insulating opposite ends of each valve from one another . a warm air blower inhibits condensation formation on the ambient air side of the valve when closed by warming the surface of the valve element . intake and exhaust filters prevent foreign material from entering the enclosure . the filters are mounted in housings located in the intake and exhaust portions of the system and have a large cross - sectional area for reducing the restriction of air flow caused by the filter . the filter is mounted in a cartridge to be easily changed in the housing . primary and secondary screens are attached to the exterior ends of the system to prevent insects and rodents from entering the system .