I have asked this, don't recall getting a response. However, on mine it comes on shortly past the 80 mark when the AC is on. If I have the EC button pushed (little light is on), then it doesn't come on to close to 90. Don't know if that's what it should do, but mine does.
I got hung up in traffic the other day and the temp got up to 100C. I was a little concerned that the cooling fan did not come on. As I had the top down the A/C was not on. Does anyone have an electrical schematic of the 1998 SLK 230?