To reduce the cabin rate of climb, which adjustment should be made?

To reduce the cabin rate of climb, closing the outflow valve faster is the appropriate adjustment because the outflow valve controls the escape of cabin air. When the outflow valve is closed, it increases the pressure within the cabin. This raised pressure effectively reduces the rate at which the cabin altitude changes, thereby slowing the cabin rate of climb.

The outflow valve plays a crucial role in maintaining cabin pressure during altitude changes. A faster closure means that less cabin air is allowed to exit, thus causing the cabin to climb more slowly relative to the aircraft's exterior altitude changes. This adjustment directly affects the differential between cabin and external pressures, ensuring a more stable environment for the occupants.

Other options would not effectively achieve the desired outcome. For instance, reducing the freon level pertains to the cooling system and wouldn't directly influence the cabin pressure dynamics. Increasing the temperature of cabin air may lead to varying levels of comfort but does not inherently affect the cabin rate of climb. Opening the mixing valve, which regulates the mixing of hot and cold air, could potentially complicate the situation by allowing more airflow, which might increase the cabin altitude change rather than decrease it. Thus, the correct action to take in this scenario is to close the outflow valve faster.