'02 Ford Focus overheat

When my '02 Focus is idling the temp gauge creeps up to red. The cooling fan only comes on if the A/C is turned on. I have replaced the thermostat, thermostat front housing and cooling fan relay. None of this has worked. Any ideas? I did just drive it from Texas to Colorado if the elevation has anything to do with it.

Try replacing the temperature sender in the radiator. It is what activates the fan when the coolant gets hot. If it’s faulty the fan won’t come on.

If the fan works when the AC is on the relay is OK.

Elevation is not an issue.

Thanks! Do you know where it is in the engine compartment? I’ve gone to parts stores that tell me they have the part but don’t know where it is on the engine. And I even went to the Ford dealership and they looked it up with my VIN and everything and it’s not where it’s supposed to be on the thermostat housing! No one seems to know where it is. They told me to go to mitchell1.com but that’s no help. Somebody please!!! It’s a '02 2.0l DOHC zetec in a ZTS model