Hi all,
Where can I locate the AC relay on a 1982 HE? I know the blue diode pack is LHS under bonnet, and fan red relay is down by the radiator but getting mixed info on the AC relay (and fuse actually)? Much appreciated!
Matt

 

My info says it is the front of 3 relays (there may only be 2) located near the right hand bonnet catch by the brake servo, sure I only have two relays in this location one of which is the starter relay, I can have a prod tomorrow as my harness is in pieces at the minute. The fuse is a bit ridiculous and is a 10A inline located in the same area.

 

I do not think that there is an aircon relay under the bonnet on a pre facelft HE V12. The compressor clutch is activated by a green wire that runs along the V and emerges from the loom. Any relays are in the cabin controlling the fans.
The fuse for the aircon is in the fuse holder under the steering wheel side shin trim. A 50 amp one.

 

Don't disagree hence the 'I will have a poke around' these are what I looked at and I do have those relays out currently for harness work. So I have the starter relay out and also found that inline fuse while doing so, there was another relay there too, was looking for a different relay (feedback inhibit) that isn't fitted and haven't identified the other yet. I'm aware that Jaguar drawings can't be entirely trusted, this is a clip from a pdf but I do have the complete Jaguar 'book set' in physical form (section 90 in vol 5) but I know for sure that is too 'new' - as it shows seat heaters and even the Jaguar security system that I am pretty sure indicate those drawings are too new.(that and all the large circuit diagrams are for 1993 or 1995 - so I use these that state 'through 1987' on them. If you have a good source of 'accurate' 1987 year I'm all ears - right now I am validating circuits the hard way starting from the Jaguar drawings I have.




This drawing shows how either the AC or the thermal switch can start the electric fan and is referred in the image above - again indicated as for 1987

 

Thanks Greg. My aux fan was intermittent - we suspect the blue diode pack and will replace when I find one- however we changed the red fan relay at the front by the radiator. Now the fan works consistently but the AC won't activate- perhaps that fan relay has a diode and/or AC clutch relay also and we added the wrong part?

 

This might help

 

No diode in the fan relay that I know of - a diode pack wouldn't be hard to create so I wouldn't stress over finding a Jaguar version - let me see if I can find the beastie and get the top off but really just need the largest current capacity diode that will fit in the space - or you could make one up if you don't care about the relay base. There's nothing special about the diodes used.

 

I think, repeat think, that your car is wired like mine, in as much as the aux fan will come on whenever the compressor kicks in, as well as coming on with the water pump inlet spout thermal switch. Not all cars were so wired, but most of the earlier ones were, I think.
So it is possible therefore, that something you have done has disturbed something in this system...
But I suggest that find the feed from along the bottom of the V that connects to and triggers the compressor, and see if that goes live when you ask for full defrost (as that should immediately trigger the compressor, regardless of cabine temps signals). This would, I think again, show if the compressor is getting the signal from the cabin unit, and if it is, the problem lies with the engine bay wiring ... somewhere...

 

My car is wired exactly as you say, thank you Greg.

 

Thanks!

 

@Greg and @BenKenobi, brilliant schematic thanks

 

This is perfect, very helpful thanks all

 

Ben
The diode pack, on the LHS wing, a blue relay looking thingy, is part of the control system of the auxiliry fan on cars of the vintage of Matts' and mine. It is so wired to allow the aux fan to run on after shutdown if the temp switch in the coolant inlet pipe is closed, and also somehow prevents feedback when it is not needed in the compressor and aux fan circuits.
I have an idea it also has something to do with the headlight washer circuit on cars so fitted.
This diagram explains what, I think, Matts has got, OEM.

 

Thank you for all the incredibly detailed information. Embarrassingly I found the issue - the live feed to the AC compressor was physically disconnected.

So the answer to my multiple questions on this subject were:- fan relay faulty, now activates with AC, and I assume will work with high coolant temps (TBC); due to continual aux fan operation with climate control, the AC is ice cold even in traffic. IF after testing the aux fan doesn't activate at high temps WITHOUT Ac, I will replace the blue diode box (I found two replacements on eBay as they are no long manufactured).

 

Nothing to be embarrassed about Matts, we have all been there! Plus you npw know loads more about the system.
The best way to check the fan thermostat circuit is to pull off the two connectors to the fan switch, then ignition on, bridge them and see if the fan comes on.
Next time the coolant is drained it is quite a good idea to replace the OEM fan switch, which goes on and off at 85°C with one that goes on at 90° and off at 85°:
https://www.ebay.co.uk/itm/387071297...Bk9SR5zb3v2NZg

 

After a 1500 miles drive across Northern Europe in the recent heat wave and I can confirm I have both aux fan activation with AC and at higher temperates (traffic post motorway) without AC; I have ice cold AC even in traffic (I have an upgraded revotec aux fan). Overall fairly limited temp gauge moves even in blistering hear. I believe the fan relay was defective in my car so it previously only came on with AC (which is most of the time anyway), we replaced that and now it activates when required without the AC.