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Aux. Fan Works Only w/ AC??

DaveWV

NAXJA Forum User
Location
Tampa,FL
Today I noticed that my aux. fan is only working when the a/c is on. It won't come on when the engine temp rises. The temp guage read 230+ and it still wasn't comming on. I turned on the A/C and the temp went back to normal with the aux. fan on. What should I be looking at first? Thanks----------Dave
 
Dave,

On the late 80s XJ with the 4.0 engine you got either a 1 core radiator and a mechanical fan OR a 2 core radiator with a mechanical & an electrical fan

The electric fan is actuated by two means. The first is when the AC compressor is engaged. The second is when the temp in the cold tank of the radiator reaches 190F.

If you look at your radiator you should see an electrical connector screwed into the cold tank (driver's side) between the Transmission cooler lines. That is the temp sensor for the electric fan.

Make sure the sensor is connected to the chassis harness. You can unplug the sensor and jumper across the chassis connector. I would do this when the vehicle turned off, then start the engine and see if the electric fan comes on then you know it in the sensor.

The sensor in the radiator is a ON/OFF switch, not a thermocouple. So once the temp reaches the correct temp the switch will close and the fan will come on.

If I recall my electric fan did not come on before 220F.

You may want to replace your mechanical fan clutch. It sounds like you may not be drawing enough air. I have heard to expect no more than 5 years out of a fan clutch. I think I'd replace the mechanical fan clutch before I worked on the electrical system.

I changed my fan clutch after an over heat caused by a broken fan belt. I could notice a big difference in the amount of air pulled by the mechanical fan.

HTH

Martin
 
Thanks martin.
The fan used to come on at just over the 210 mark. In fact I know it was running just a few days ago without the A/C. It must be the sensor. I'll check it though. Thanks----------Dave
 
Not necessarily the sensor. I need to confirm with a wiring diagram and I'm on my way out the door to a class, but I believe the switch in th radiator tank connects to a relay and the relay is what turns on the fan. There are two plug connections in the circuit -- one is at the fan, and that one muct be good if the fan works with a/c. The other is between the radiator sender and the relay -- check that one. In fat, as a quick check you can unplug it and see if the fan works if you jumper it. If so, the sender is bad. If no, the problem is somewhere between that connector and the fan.
 
i myself just unplugged the connector and rigged a switch to short the circut manually from the driver's compartment. this was to temporarily cure my bad radiator problem but i liked it and kept it. after i get a 3 row GDI radiator i didn't need it much but it is just an idea. inexpensive at that. if you want any pics lemme kno i'lkl try to get em up
 
Dave, I did the same thing that Dent did. I put in a manual toggle switch, one with a light. That helps me remember in the event that I forget to trun it off. I also have a 87 XJ, and I got rid of the old cooling system and upgraded to a GDI 3 core. I think I paid $100.00 for the radiator from 1-800-radiator. I really like having the option to run the fan when I want too. Hope this helps,

Casper
 
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