Seems to me that the e-fan running whenever the compressor is operating might potentially improve A/C performance in traffic conditions by helping to pull air thru the condenser, yes?
Anyhow, and just FWIW…
My car (which is a V12 conversion) is running the original 6-cylinder e-fan circuit. That is, the e-fan is temperature triggered only. No problems with either engine cooling or refrigeration in traffic conditions. The temp switch triggers the e-fan relay at about 200F/93Cº…which means the e-fan doesn’t come into play all that often.
The system is designed to engage the compressor clutch (and thus trigger the e-fan) whenever the climate control system is in use, even when heating is called for, at least thru 1988.
Ahh, that makes sense, i think that IS what happens. I have rarely driven my car in the cold, so ambient temp is always higher than what my setting is.
I guess i wanted to point out, its not the compressor but the climate control that turns on aux fan.
Kirbert
(Author of the Book, former owner of an '83 XJ-S H.E.)
44
I think he was pointing out that, no, it’s the calling for compressor operation that turns on the aux fan. You have removed the compressor so there’s no compressor to operate, but it’s still the system calling for the compressor that brings on the fan. If you had a compressor, sometimes it would cycle off, and the fan would cycle off with it.
The same “+” voltage signal that triggers the compressor relay also triggers the e-fan relay…so the two operate in tandem.
Unless… the coolant temp is high enough to close the e-fan temp switch, in which case the e-fan will operate without the trigger from the climate control system.
But what I was trying to point out, actually, is that the e-fan has no idea what temp you’ve selected with the climate control dial. For that matter, neither does the compressor.
I’m suspecting that may be why Supeblue came to me with a “stuck” aux. fan. She was originally a Mass. (Hyanis, near the coast) car, and although I’ve never been to the NE area I have a hunch there would not be much need to run a.c. there vs. just putting the windows down when the temps are a little on the warm(er) side. Certainly the outdoor temps would not run hot enough also for the fan to need to come on, on its own … It has gotten over 100 deg. here of late in Dallas (105 today) and the temp gauge still shows to be in the normal range.
With both thermostats out 5.3 v12 runs cooler. That’s confirmed and re-inspected with thermal camera. Confirmed at idle and at 2500rpm
I’m not a big fan of Jaguar V12 engine. I’m not a fan of it at all - to be honest… However I know big psycho who was trying to make 5.3 more durable (i think concept was changed to v12 2stroke conversion). These engines are cheap as sand in UK, where sand - by weight seems to be actually more expensive. Not sure about bypass mentioned above - please be aware that every engine has some sort of bypass for the comfort of those in the cabin. Lower working temperature preserves everything in the engine. Unfortunately it drains some caps from your wallet (fuel consumption). It’s some sort of method if you want to preserve your XJS slightly longer… Don’t need to mention that v12 shouldn’t have thermostats by default (i know, i know… 5.3 overheating issue is just a gossip…)
Peter, there is a mobile phone called Cat S61. Have a look. You can record movie, take photos and map temp of those at any point (or rather pixel). You can literally see which cylinder is overheating and which is’t working as well…
I’m no electrician, but I don’t even see the a.c. compressor in that circuit. It does though look like whenever you switch the a.c. on the auxiliary fan comes on and, course it comes on whenever the coolant temp is up high enough to trip the fan switch. What is the run-on diode for, though? Is that so the fan can continue to run even when the ignition is off if the coolant temp is still hot enough to trigger the switch?
Yes, just that. At the left is feed [38] from the battery, on the right is feed <33> from the ignition. When then the relay is energised it allows the battery power to provide the feed for the fan and also a feed for the relay via the diode. As long as the thermal switch stays closed, the fan will run, even if the ignition feed is disconnected. When the switch opens again, the relay drops out and can no longer supply the battery feed to the fan or to the override. So the fan does not come on with the ignition off, even if heat soak causes the switch to close again.
MY wife’s ’92 ops exactly as the diagram indicates and she never turns the A/C off. When the car starts up with the A/C on there is no Aux fan until the coolant temp switch closes and turns it on via the aux fan relay. It will remain on until the coolant temp drops enough to open the coolant temp switch – then it will remain off until the coolant temp switch again closes again at the given coolant temp value and so on as needed. There is an over-run feature that keeps the Aux Fan on and running (via the coolant temp switch and power to the fan control relay ) if you should shut down the engine - or shut down and pull the key out - if the coolant switch is still closed, and will continue to run until the coolant temp drops below the coolant temp switch turn on point. This OEM scheme also allows the Aux fan to turn on whenever the coolant temp switch closes regardless of A/C operation ( On or Off, and the overrun feature is still active).
Certainly the outdoor temps would not run hot enough also for the fan to need to come on, on its own … It has gotten over 100 deg. here of late in Dallas (105 today) and the temp gauge still shows to be in the normal range. 
It does though look like whenever you switch the a.c. on the auxiliary fan comes on and, course it comes on whenever the coolant temp is up high enough to trip the fan switch.