The control determines the type of free cooling changeover based on which sensors are present and reliable. Conditions include the following items:
- Operational space temperature and operational outdoor temperature = dry bulb changeover
- Operational space temperature, operational outdoor temperature, and operational outdoor humidity = single enthalpy
- Operational space temperature, operational outdoor temperature, operational outdoor humidity, and operational space humidity = dual enthalpy
- If the operational outdoor air temperature value is unreliable, free cooling is not available.