Hi Brains trust,

The Auxiliary Fan on my '85 XJS V12 HE has never worked since I acquired the car. She runs cool, which is great, but it's something I want to fix.
On doing some electrical testing today, I took the small wires off the temperature sensor at the front of the engine and confirmed that when the car is running, AC on (it's not cold, but that's another topic for another day), but I can confirm that I have 12V across the two wires. Also, when I jumped them directly together, I expected the fan to start. Unfortunately it doesn't run. As this is a separate circuit controlling the fan, and the circuit has power, but I have no running fan, can I expect that this is a fan issue and I need a replacement? I'm trying to follow the manual's diagnostic suggestions about testing the Aux Fan relay, etc, and I get the "click" when I switch on the AC (temp at 65), but a bit lost with this circuit.
Appreciate next step suggestions. A couple of pics of what I checked today.... A paperclip is a very handy piece of equipment in the toolkit!

Temp sensor at front of engine with wires to Aux Fan circuit.

Jumping the two wires from the temp sensor, which I believe should switch on the Aux Fan.


Thank you,
Adam

 

There is an inline fuse to the fan, and also a fuse in the black box on the LHS inner wing. Frontmost one, so check these first. also check if, thermo switch wires paperclip connected, to see if there is 12v going into the fan.

 

Check the fuse as mentioned but also give the blade a good wiggle front to back.. the bearing in the front of the motor can fail and allow the center spinny bit (technical term) to jam up against the side of the motor housing. That's how mine failed at least, it would still spin in this state and would occasionally come loose on bumps, making horrid scraping sounds.

I opted not to fix it and instead ditched the fan and the condenser (my a/c compressor is long gone anyway)

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Hi Greg, testing both the in-line fuse (which is held above the Aux Fan, mine has Red wires going to it), has no power when car is running and AC set to 65 / Auto. I also checked the No 1 fuse in the fuse box on LH front wing, no power there either, as it is obviously part of the same wiring as the in-line fuse. I can see the wires then go into a group of cloth-bound harness wires through to the back of the engine bay on the LHS and some of them into a relay(?). Any thoughts on next test, really appreciated. I want to keep things original, but just need to work out what is not functioning before I buy "bits". Thank you, Adam

 

There is also a fuse in the main fusebox under the steering colum accessed through a hatch in the shin level trim. No II which controls the aircon, horns, and screen washers too. If any of these work that fuse is OK. Attached is the circuit diagram.
As you can see the red wire from the fan joins to the proper loom colours after the fuse. The black from the fan goes to earth, worth checking that it does.
Have you hotwired the fan to make sure it does work, by the way?

 

Thanks Greg, I will delve deeper. Appreciate the suggestions. OK, so the A/C comes on, but needs regassing. Also, the horns work, so that fuse must be OK. (Not ever used the screen washers). And yes, I can see where the black wire to earth goes, which is screwed into the radiator or radiator support, but looks (normal). Can I jump 12V straight to the Aux Fan? I have a spare battery and can get some wires to do a check. And finally, I need to learn to read an electrical diagram! Thanks for sharing.

 

Yes, jump your spare battery + to the red wire of the fan and the black wire to the spare batery negative. To be sure nothing fries on the car, disconnect the car battery.