Aux electric fan..controlled by AC or not?


I have an 85 XJS v12HE US market…my aux cooling fan only runs based on a temperature switch. When engine becomes hot…it kicks in to offer additional cooling…and runs for a minute or two after engine is shut off.

Talking with another gentleman with an 86 v12HE …his aux cooling fan runs constantly whenever the AC is turned on.

I realize that either car could have been modified by previous owners…or could be different by model year…

Can anyone offer any insight into the original operation? I don’t see anything in the electrical schematics which shows a direct connection to the AC system for the aux cooling fan.



Indeed Gary, also on my 86 V12 XJ the Aux Fan runs whenever the A/C is on.
The A/C red relay by the radiator powers both the A/C Clutch and the Aux Fan.

Hope that helps,


Thanks for the feedback…so either they made a model year change or my car has a failed or modified circuit. I will look into that red relay.



My '88 XJS e-fan was temp switch and a/c operation as well, the later coming from the compressor circuit. This meant the e-fan operated virtually at all times…as the a/c compressor is engaged virtually at all times.

I think all the HE XJSs were this way until 1989-ish, at which point other schemes were developed


If fan runs from the temp switch then red relay is OK. Check “blue box” (looks like relay) diode pack on left fender under bonnet… I’ll post schematics when I’m back home