I have the same issue with my S80. No solution yet, but looking... Did you find the problem?? On mine, the cooling fan does not come on when a/c is on. It does come on when coolant temp increases as it should. Apparently the relay or sensor for the a/c is broken. Any idea were these would be located?

I'm having a similar problem with my 2009 S80. There are two fans. The larger right fan will occasionally come on when engine idling at high temps (radiator cooling). Smaller left fan never comes on (AC Cooling?). No fans when AC is on and parked -- so AC stays hot. I'm looking for a way to troubles...

This was a very helpful post. I needed it to understand why my MAP sensor replacement wouldn't "take". Rather than disassemble and trim, I fixed it by using a toothpick to put a thin layer of plumbers silicon grease on the edge of th blue silicon piece. This allowed the sensor edge to work...