E-Fan question

My XJ got alittle warm about 220-230 so I pulled over to see if the electric fan kick on and it did not. So I turned on the A/C to see if the fan would come on and it did. With the A/C on and the fan the temp came back down to 210. What would cause the fan not come on? But work when the A/C or heater is turned on? Also this is a 94, and I have replaced the t-stat, and rad with a 3-row.

The engine coolant temp sensor is read by the PCM...so when the sensor says coolant is too hot, PCM activates fan relay. ( a different sensor connects to your guage)

A/C request is also read by the PCM to activate fan relay.

So, my guess is coolant temp sensor, or associated wiring is the problem.

I have heard that some people solder a resistor in parrallel with the sensor to cause the fan to kick on a little sooner, temperature wise.

i had the same problem , i replaced the thermostate
and installed a fan switch ..just in case..