If the sensor isn't working, your fan won't turn onbecause it won't know that the temperature is hot enough to require activation, which can frequently lead to overheating.

 

Like Jamal360 mentioned, it may be the temp sensor in the rad. After an overnight cool down with a scanner check the temperature readings from the rad temperature, engine temperature and intake temperature. They should all agree within 1 degree. If one of them is skewed you have to correct that. As for the A/C, it will not cycle on if there are any cooling system problems.