Dodge Neon cooling fan not engaging

Hello I have had some ongoing issues with this car the last 3 years over overheating,
I have like clock work been replacing my thermostat in the line, well this time I replaced that danged thing again and the heating was still an issue, (yes oil and coolant filled. ) so I replaced the sensor in the motor and the fan would still not engage . so I pulled the fan and connected direct current to the fan and it did indeed start right up. so its not the fan motor, I hooked a direct current where the ah hell mental block here the plug sensor by the fuse, that was replaced, and yet still no fan engaged… Here is the rub, If I have the AC on the motor fan will run… Soooo Now I am asking for Ideas? I am still reading a sensor malfunction on the computer, So I am now sending out an SOS or a SOD Save our Dodge ?

Did you replace the correct coolant temp sensor? This car should have two, one for the ECM, one for the gauge.

I replaced the one in the block. and the one in the fuse box, what is the ECM?

It is probably driven through a relay. Find the schematic to that car and short the contact to see if it wants to turn on. Then work your way back, towards the sensor.

Have you replaced the relay?

If the fan runs with the A/C on the relay is working. How hot does it get with the A/C and fans on?
With the A/C off the cooling fan should turn on at 220 degrees.

There is only one coolant temp. sensor, it is on the back of the cylinder head.

What year is this car?