overheating electric cooling fan not comming on

I have a 90 jeep cherokee. the engine is overheating. The electric cooling fan is not comming on. It will come on if the ac is on. has anyone had this problem?

Hey,
I've had the same problem and replaced my ratiator and my thermostat and that fixed the problem a little bit now I run about 210. Still little hih but its heck of alot cooler then what it was running

210 is normal operating temp, don't worry about the engine running at 210.

If your electric fan will not turn on when the water temp gets hot then you probably need a new temp sensor.

My cherokee is an 89 and I rebuilt it from ground up looks pretty good everyone I show it to says it looks like a 94-97, I hope to get pics of it soon. I did have to replace the temp sensor BTW :sunglasse

I too have a problem with my electric cooling fan in my '90 cherokee (4L c/w AC). However mine is wierder.

The fan will not come on with AC, or when it is hot (unless it has to be really hot before the Rad sensor closes).

The Fan is fine. The fan relay is great. The AC clutch relay looks OK. The only thing I can't figure out is if the diode block is functioning (I can't find the darn thing).

I am not sure if the rad temp sensor is OK. Should it be completly OPEN (no resistance) or should it have some resistance at all times? What temp is it supposed to close at?

Even if the rad sensor is OK, why wouldn't the AC trigger the fan?

Why am I not able to figure this out? (yeah, okay I am an idiot!)

TIA for any help:confused:

I replaced the fan sensor in the radiator. It only over heats when it is not being driven, as when at a red light. the fan used to come on at 220 degrees. Now it is not comming on. Does anyone have a wireing diagram for a 90 Cherokee. Also does anyone know where the relay is for the cooling fan?

thank you

Here is a wiring diagram for the cooloing system, hope it helps. It all seems to be close to real on my '90 Cherokee, except I can't find the diode block

the wiring diagram was a big help. I have checked the voltages on everything and it appears that the diode asembly is the cause here. I just need to find it.

Yeah, I was thinking the same thing. But my water pump was leaky so when changing it I also changed the thermostat and took the temp sensor out of the rad and threw it into a pot of water and boiled it. Lo and behold when the water boils the switchcloses, so I now know that it works.

I still am not convinced that everything works OK, but I do know this. The engine is running 10-15 deg Celcius cooler and after some more work last night (on the A/C) I know that when the A/C is engaged the fan comes on.

I still have not got the fan to come on via the temp switch but I figure that I know it works, and the temp switch is in the rad (right by the lower hose) and it is measuring the coolant temp there, not at the block, where the temp sensor is for the gauge.

I too am still trying to find the diode block, let me know if you discover where it sits.