Discovery Series II & Range Rover
WARNING: This page is about a different car, the 2002 Land Rover Range Rover, 2002 Land Rover Freelander, and 2002 Land Rover Discovery. However, it is still accessible from the selected car via links, so may be relevant.
When A/C switch is turned on, an A/C request signal will be seen at ECM 40-pin connector C0637 terminal No. 16 (Yellow/Gray wire) and terminal No. 38 (Yellow/Black wire). The operation of the ATC request is via A/C switch being connected to ground.