Air conditioning system comprising a system to control freezing of a heat exchanger of an air conditioning loop

The system has a control device for controlling freezing of an ambient air/cooling fluid heat exchanger (10) comprising two passes (P1, P2), and a temperature sensor (20) arranged in a zone situated opposite to one of the passes. The temperature sensor is placed at distances (X1, X2) from a separation line (27), where the distances are less than 66 percent of respective widths (L1, L2) of the passes. The temperature sensor is arranged downstream of the heat exchanger along a flow direction of an ambient air flow (11) through the heat exchanger. An independent claim is also included for a method for determining freezing state of an external surface of an ambient air/cooling fluid heat exchanger constituting an air conditioning system.