1985 xjs
Sometimes when I start the engine, or most times, and pull away turn on the a/c evan to demist there in no fan or engine auxiliary cooling fan, no compressor, then after about 1-2 mins it starts and is OK for the whole trip. Could this be the amplifier adjustment or interior temp sensor.
rex647,
It sounds like the Delanair MK II system in your 1985 XJ-S is working exactly as it was designed. Do you have a copy of the Drivers Handbook for your car, or the XJ-S Repair Operations Manual (ROM) to read up on how this climate control system works?
Paul
Cheers Paul, I don’t but I will, 
There is a coolant temperature sensor in the Delanair MK II that keeps the fans off until the coolant reaches a certain temperature then the fan relays kick in. You can bypass some of the automated features by selecting Defrost on the mode selector switch. This will allow you to operate the blowers even if the engine is cold and not running.
Paul
Cheers Paul but even the defrost doesn’t kick it in, perhaps it’s that sensor that is faulty
That could be a failed C46179 relay (actually four relays in one black box) that controls the fans or perhaps one of the Mode Selector microswitches.
Paul
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Quick catch up on this.