Turning on the A/C, especially in traffic, may temporarily bring down temperatures as the auxiliary fans are always on when the A/C is on to move air past the condenser and hence also move air past the radiator. However, this will only be temporary and you'd notice the difference at idle with no load on the engine. A/C usage actually increases the load and heat output of an engine as the compressor is putting a decent strain on the engine when it kicks on.
Additionally, a lot of A/C systems will shut off above a certain RPM anyway to save the strain on the compressor and it may not really kick on at the track - although I haven't confirmed there is a shut off at a certain RPM on the E9Xs.
I do turn the A/C on right away after I come out of a session though as it turns the fans on while I'm idling around and going through the pit and paddock and brings more air through the radiator at low speeds. At high speeds and high loads on the track, I don't think the A/C will help too much... But it's worth trying if someone wants to.
CSL replicas are now CSL counterfeits. Jesus saves, like Valentine1.