Refrigerant Pressure Sensor
WARNING: This page is about a different car, the 2000 Mercedes-Benz C43, 2000 Mercedes-Benz C280, 1999 Mercedes-Benz C43, and 1999 Mercedes-Benz C280. However, it is still accessible from the selected car via links, so may be relevant.
The refrigerant pressure sensor is located on top of receiver-drier. The sensor protects the A/C system from an under/over charge condition, excessive pressure, and also controls the auxiliary fans. See Fig 1.