A/C Clutch
WARNING: This page is about a different car, the 2010 Lincoln MKX and 2010 Ford Edge. However, it is still accessible from the selected car via links, so may be relevant.
An electromagnetic clutch is energized when the clutch cycling pressure switch closes. The switch is located on the suction accumulator/drier. The closing of the switch completes the circuit to the clutch and draws it into engagement with the compressor driveshaft. When the A/C is engaged, EPC pressure is adjusted to compensate for the additional load on the engine if the Electronic Throttle Control (ETC) signal is not available.