A system for controlling the ventilation of an enclosure such as a poultry or livestock house is disclosed. The system includes a ventilator mounted in a wall of the enclosure. Pressure difference between the inside and outside of the enclosure created by suitable fans, causes a flow of air to pass through the ventilator. A sliding door assembly controls the amount of air which passes through the ventilator; the sliding door assembly is operated by a pressure-sensitive actuator switch. When the pressure difference exceeds a preset pressure range, the sliding door inlet assembly is opened slowly until the pressure difference drops within the preset pressure range at which point the sliding door inlet assembly is halted. When the pressure difference drops below the preset pressure range, the sliding door inlet assembly is closed slowly until the pressure difference rises into the preset pressure range at which point the sliding door inlet assembly is once again halted. Limit sensing switches are also provided to halt operation of the door-operating mechanism at the fully opened or fully closed positions.
