1984 XJ-SC 3.6 manual

Hello All, I notice that lately I can turn on my a/con with the ignition switched off ! I suppose it’s a faulty relay or something similar - if so,where would it be situated ?

also 1966 MK 2 3.8 Man.O/D


Is it the entire climate control system that powers up with the ignition off? Or just the fans? Or…?

My initial off-the-cuff thought is that there’s a problem with the mode control switch.

I’ll need to do some mulling…which may take some time. Others will surely chime in sooner.


Is that something you have just noticed or something that you’ve just noticed and you are sure it wasn’t there before? Just asking, some skilled vehicle technicians are focused on making something work again, with exclusion of details… This seems to be a standard repair workmanship in UK :wink:

Morning All, Sorry,should have mentioned the following - this has happened in the past,but corrected itself over time,but has just started again. Also it is only the fans coming on when I turn the switch


Sounds to me like a climate control module issue. The module is buried on the right side of the tunnel. After you’ve gone through the trouble of fishing it out, the next problem will be finding someone who can diagnose it and then fix it.

The fan relays have constant 12v “+” and constant ground/earth. They relay on “+” voltage from the servo to operate and switch the fans on.

Naturally the servo is not intended to be operational with the key off.

On the basis of ‘you gotta try something’ I’d disconnect the brown wire from the mode control switch and see if anything changes. The brown wire is constant 12v “+”. If there’s an internal problem with the switch the brown wire might be feeding the system of with the key off. Might not be easy to access the back of the switch…been a long time since I’ve been there and done that.