Radiator Fan Controls

[jfjharry]

1973 2+2 Series 3.
I have just noticed that one fan starts when the ignition key is turned [motor not started].

I read in a previous topic "V12 Running Hot" that a reply by Peter Crespin says that a lot of fan controls have been modified.
By looking at the wiring diagram there should be only one thermostat control relay therefore both fans start together.
Mine has two cooling fan thermostate relays; one newer than the other which looks original. I can only see one thermostat.
Without pulling the wiring apart its difficult to see where the wires go.

My question is: as the vehicle was imported from Arizona USA could it have been wired so that one fan starts straight away? I doubt this very much but would like to hear some expert knowledge.

I also noted the mention of an Otter switch - is this the thermostate switch

[MarekH]

Dear Harry,
If the fans come on separately via independent relays, then this is an aftermarket alteration by a previous owner ("PO"). For non airconditioned cars, the oem solution is to have one relay and one thermostat (made by an English company called "Otter") to control both fans together. For airconditioned cars, there is a second relay which will override when the aircon is on. Both fans operate together in each case.

The relay coil windings would green for power and black/red to the Otter switch. The other side of the Otter is grounded to fire the relay when the water is hot enough. The relay power connections for the fans are brown (with an in line fuse) when on, black earth when off and the common black/green terminal to the fans.

If the PO thought it worth altering, you may wish to review how well the cooling system is working generally. It may be the case that you have an airconditioned setup, but only one fan works.

A properly working system wouldn't have needed to be altered.

There is a wiring diagram for US spec cars on the xke-data website.

kind regards
Marek

[PeterCrespin]

1973 2+2 Series 3.
I have just noticed that one fan starts when the ignition key is turned [motor not started]. I read in a previous topic "V12 Running Hot" that a reply by Peter Crespin says that a lot of fan controls have been modified.

Check you don't have the fans wired through an extra hidden switch for manual control - of OTS models it's often the redundant rear window heater switch but it could be a mystery toggle somewhere under the dash etc.

More inportantly, beware any twin fan system where only one fan runs, if the shroud does not have a partition down the middle separating the two areas behind the radiator served by each fan. This separating fin should almost touch the back of the radiator core or touch it with a bit of foam or rubbed to prevent chafing the fins. If you don't separate the two halves of the rear shroud,then if one fan stops the other one just draws aire through the dead side of the shroud past the stationary fan blades and practically no air is pulled through the core itself.

Pete

[jfjharry]

Thank you Pete & Marek
I now understand the workings of the fans better. I checked all over mine for a hidden or alternate switch but could not find anything. While trying to chase through the wiring I noticed an old plug on the new fan side. I unplugged the new edition and plugged the fan into this old plug, both fans then come on together when the air con was turned on. I then went for a test drive and both fans cut in and maintained the temperature at the 'normal' level. I think I have fixed my query although I cannot understand why they went to all the trouble of modifying one fan to come on with the ignition switch especially when there is no extra divisions between the fans to prevent what Pete mentioned.
Thanks once again.

[PeterCrespin]

I didn't know you had AC.

The AC would probably be wired to have one fan come on when the compressor is in circuit ,so that regardless of overal engine temp, AC on means fan on, to ensure the condenser condenses. It may be some back-to-front wiring or something, or the fan only came on with ignition because at the time you had the AC switched on, which would make the fan run even without the engine running.

Anyway, it's fixed, that's the main thing. Well spotted.

Pete

[MarekH]

No Pete,
With aircon, the oem setup still wires the fans in parallel. All the second (aircon) relay does is over ride the Otter to make sure the fans are on any time the aircon is on.
kind regards
Marek

[PeterCrespin]

Fine - thanks for the correction. Never had a E or Series XJ with AC. I think on some later XJs with twin fans, it sets one of them spinning, or maybe an aux pusher on the front of the condenser. Never had such a car though. Suspect your 'busy vee' won't have room for a compressor in there will it?