WARNING: This page is about a different car, the 2024 Audi S6 and 2024 Audi A6 Quattro. However, it is still accessible from the selected car via links, so may be relevant.
Fig 1: A/C Refrigerant Low Pressure Switch
Courtesy of AUDI OF AMERICA, LLC
Function:
Switches off the A/C compressor when there is a decrease in the refrigerant circuit pressure (approximately 2 bar (29.01 psi)).