Odd temperature while driving fast with AC

I posted operation of the cooling fan it can cycle based on a/c on or off speed your traveling temp etc.If the engine is left to idle the cooling fan will come on at just over half way on the gauge on that car.The problem is saturn started using one coolant temp sensor instead of two they use to use one for the gauge and one for the computer.Then they started using just one for the gauge and the computer problem with that is the one they were using is the same one they were using just for the computer when they used to use two the gauge temp sender hardly ever failed.But the one they used for the computer had a very high failure rate.But at least when they had the one for the temp gauge you could tell the one for the computer had failed because they always read colder then actual temp and you could see on the temp gauge the car was running too hot and the fan wasn't coming on when it should.Now with one sensor that fails all the time you wouldn't know it was running too hot unless your car was boiling over.I have a 1999 SL2 and i replace mine every couple of year's.Your best bet is to just replace the coolant temp sensor there only 10 and they cause all kind's of symptoms when they fail from******** dieing surging over heating no starts etc.Its located screwed into the head of your engine just below your upper radiator hose.Also unplug the coolant temp sensor and inspector the connector side that goes into the sensor if the terminals are blue or green you will have to replace the connector too.Also when you turn on your a/c your radiator cooling fan comes on?Look under the front of your car right below your a/c condensor you should have a black flap hanging down from your splash shield to scoop air into the a/c condensor and radiator do you have one of those?