Electric Fan Not Running

No matter how hot the engine gets the electric cooling fan will not cycle on. I can turn on the A/C and the fan runs fine, so I know that the fan is OK.
Question: Is the temperature sensor that is on the back of the cylinder head what kicks the fan on when the engine reaches a certain temp? Do you think that might be the problem?

So far I have installed a new relay and the temp sensor that mounts next to the fan that goes into the radiator. These were apparently not the problem.

(1989 Jeep Cherokee in line 6)

Thanks!

My 1988 Jeep Cherokee fan switch is located on the driver side of the radiator. Try removing the cable attached to the switch and shorting the pins. If the fan turns on, the switch is bad. If the fan doesn't turn on, maybe it's a bad fuse or relay. In my case, the fan runs fine when the pins leading to the radiator switch.

Does anyone know at what temperature the switch should close normally? Does anyone know where I can buy a switch that turns on at 210 degrees?