My 2004 Jag S-Type does not overheat but will not kick on high speed when the A/C is on. It cools great going down the highway, or when first started when the engine is cold. In traffic or sitting still the A/C get shot an dI am assuming this is due to the fact the cooling fan is not kicking on high to cool the condensor.

I noticed that the radiator cooling fan never kicks on high like it used to. Is there a way I can test this? Is there a common issue such as a fuse, relay, or control unit that affects this?