Here's what others have written: "The coolant temp sensor is at the bottom of the radiator."
At that many years crud can accumulate and insulate the temp sensor. You may have pump and other issues as well but the cheapest thing to try is the most aggressive radiator flush you can find. Shops used to have a machine to do this but I haven't seen one in years.
If you have the time, here's the full rundown of how to test this part:
There's a 1999 Pontiac Grand Prix a family member of mine owns and we've been trying to get it working for a trip he's going on. My main question is how we would get these fans working without him having to keep the air on?
We've changed the thermostat, the sensor, and while looking at the fuses I found this car has five fuses to control the fans. He bought one of the fuses and replaced it and the fans still wont run without the AC. Should we replace the other two that might be bad? I've called the part houses and they each tell me they don't have the other fuses. Where can I get the other fuses? Could there be anything else wrong besides the fuses?
Any help and all help is welcomed
Thanks to all that helps.