1991 Buick Park Avenue radiator fans temperature sensor

Slow to stop up moderate hill temp rises to 240* - stays high when driving on flat-park car-let cool-start car -temp rises 240*+ fans do not come on. Start inside air conditioning & both fans come on- shut off A/C & fans go off- where is the temp sensor located( how hard to change)?- I believe it is that sensor & not Thermostat-but I do not know squat.
Kurt
My wife drove car & it wouldn't start. She had it fixed-couldn't find bill but said they had to take steering column apart to fix. I drove 60 miles no overheating, stopped ( park & idle ) to get directions came out & engine is stopped-would not start. Parked it (pushed) let sit couple hours & it started. Over next few days drove it no more than 3-4 miles & it only happened once. Then headed home & this is when went up hill & it started heating up. Then I parked, let it sit 2 hrs it started-I got under way for 5 mins & it overheated & stopped- towed it home & next morning it started right up but in idle overheated again & stopped- which is when I checked the fans. Before the temp while running was always 200*. Could it be a soldered wire in steering column?