The control action of a reverse acting thermostat is to:

In the context of a reverse acting thermostat, the control action is designed to provide cooling or to turn off a heating system in response to temperature changes. When the temperature rises above a predetermined set point, the reverse acting thermostat responds by opening the system. This action facilitates cooling by allowing cooler air or fluid to enter the space, which lowers the temperature back down to the desired level.

The purpose of a reverse acting thermostat is to maintain a comfortable and stable indoor environment by preventing overheating. When it detects a rise in temperature, its opening action effectively helps to regulate and control that temperature by initiating cooling mechanisms.

In contrast, options suggesting closing the system when the temperature rises or opening/closing when temperature drops do not align with the operational principle of a reverse acting thermostat, as they would not effectively manage the cooling process in response to increased heat.