Ambient Air Temperature (AAT) Sensor
WARNING: This page is about a different car, the 2016 Ford Transit Connect. However, it is still accessible from the selected car via links, so may be relevant.
The Ambient Air Temperature (AAT) sensor is an input to the PCM. If the temperature is below approximately 0 °C (32 °F), the PCM does not allow the A/C compressor clutch to engage.