francoismarking

I have a 2006 C280 that is overheating. It starts fine, runs fine, and sounds fine. But when I am in slow traffic for just a little while it gets very hot. So hot that the aircon shuts down. When I'm on the open road at about 100km/h it cools down to normal again. I've replaced the thermostat and heat sensor sitting at the back of the engine, but no luck. The fan turns on when it is cold and the aircon is on, but not at all when it gets warmer. Is this a faulty fan? The tester at my local dealer shows another temperature switch on the front of the engine is faulty. I have no idea where it is. What else can I do?