In a vapor-cycle cooling system, the role of the outflow valve is primarily to:

The primary role of the outflow valve in a vapor-cycle cooling system is to regulate cabin pressure. This is crucial because maintaining the appropriate pressure within the cabin is essential for passenger comfort and safety, especially during flight. The outflow valve opens and closes to allow the excess air to escape from the cabin, which helps to maintain a consistent pressure.

While aspects such as air temperature and the introduction of outside air are important in cabin atmosphere control, they are not the primary functions of the outflow valve. The outflow valve does not manage freon levels directly; instead, it focuses on balancing the pressures within the cabin environment. Thus, effective regulation of cabin pressure is key to ensuring optimal operation and comfort within the aircraft's cabin.