I'm currently fixing up the air con in my 3.6Lt '88 xj40. I've had the system re-gassed, new receiver dryer and today replaced the thermostatic switch in the radiator as well as giving it a flush and a refill with nice new coolant.

Now I'm wondering if anyone might have a copy of the diagram in order to modify the wiring so that the Auxiliary Cooling Fan operates when the A/C is turned on?

 

I'd be interested in the re-wire instructions too.

 

I discovered these instructions on another forum courtesy of Steve Randall and others. I have also learnt that the modification can be performed by installing another relay which serves to remove the need for an in-line diode although I can not seem to find clear instructions for performing the additional relay modification...

HI Mike and the List,

Hi List, Here is a procedure for adding the diode so the aux fan comes on
with the compressor. This mod will cost less than $10.00. It will lower
high side pressures on cars with R-134a by 30-50 lbs when the car is not
moving, greatly enhancing cooling when stuck in traffic, and keeping the
system from blowing the hoses and seals out. It is even beneficial to R-12
and R-406 cars. The parts and supplies need are readily available at any
Radio Shack or any electronics parts house.

Tools Needed: Soldering iron, crimping tool, wire strippers, pliers
Supplies needed: Solder (rosin core), 2 feet of insulated wire (recommend 18
gauge), diode (1N4001, 1N4002, 1N4003) or equivalent, heat shrink tubing
(assorted sizes and lengths), some type of disconnect crimp-on connectors,
male and female (spade type will do, bullet type better, aviation knife type
best but hard to find, a couple of 3-way splicing connectors if you don't
want to cut any wires).

Procedure:
1: Disconnect the negative battery cable. You will be working with/near
wires that may have power applied even with the ignition off
2: First of all, locate the wires you will be splicing in to. On the A/C
compressor side, it is the 12 volt wire going directly to the compressor
clutch. On my car this is a green wire going directly to the clutch plug.
This is one of the two you will be tapping into. Do NOT use the black wire as
this is ground (earth). Next, remove the plug going to the aux fan relay
(normally a red Lucas relay or maybe a black Bosch one like mine). It's on
the left side near the top of the radiator support frame on the engine
compartment side. Next locate the Green wire with a white stripe going to
this relay. It is the one farthest to the right when plugged in and mounted
normally. This is the other wire you will be tapping into.

2: Next, make up the diode harness. Cut the length of spare wire in half,
strip one end of each wire and solder one piece to each of the two leads
coming out of the diode. (If you don't have soldering skills or equipment
you can use red butt type crimp connectors here, just make sure they are
tight). Identify the "cathode" end of the diode. It is the end with the
marker band around it. Tie a knot or otherwise mark the wire attached to the
cathode end as not to get them confused later. Then take a piece of heat
shrink tubing just big enough around to slip over the diode and long enough
to cover all bare wire and heat it to form insulation around the diode.
Repeat this process as to end up with two layers covering the diode and
exposed wires.

3: Connect It. Using the three way splicing connectors or other means that
you like, connect the end you marked or tied the knot in (cathode) to the
green/white wire you located previously which goes to the connector to the
fan relay. I like to use disconnect type connectors somewhere in line here so
this can be disconnected for any troubleshooting that might be needed in the
future. Next, connect the other end of the wire attached to the non-banded
(anode) end of the diode to the green wire previously found going to the
compressor clutch plug, making sure the wire is routed so that it will
interfere with nothing else.

4: Test It: Reconnect the negative battery cable. Turn the Climate control
off. Start the car. Verify the Aux fan is not running. Turn on the A/C.
Verify the aux fan is running. Turn A/C off with car running. Verify the
Aux fan is not running.

Notes:
1. No additional fusing is needed as this mod simply uses the compressor
clutch power to activate the relay that powers the aux fan.
2. Some Jaguar schematics show a diode in exactly this position for this
function, although some show it opposite polarity than is needed, (a misprint
I'm sure). Some later prints show it correctly.
3. Apparently, some cars come like this from the factory, mainly 12 cyl
versions.
4. This is a first draft of this procedure and I've made every effort for it
to be complete and correct. I certainly welcome any corrections,
clarifications, or better ideas.

Steve Randall
85XJ6 with COOL A/C


I would add one more test. Disconnect the aux fan thermal
switch (in lower right of radiator), and connect the wires together to see
if the aux fan still comes on thermally, and of course does not turn the
A/C clutch on. A bad diode would pass the first test but fail this one.

 

Jagfix38

I found a post as well on another site and sent an email to two of the posters for the instructions. Haven't heard from either of them yet, but I know I will. I'll post it in the string when I get it. I think it may be the technique you were referencing.

 

Jagfix38

I have attached the doc I mentioned previously. I hope you can understand it and interpret it for me, I'm horrible at understanding electrical schematics.

This is not my diagram, credit to a gentleman by the name of Nigel.

 

I have attached a revised wiring diagram, which has more detail.

 

Thanks for finding and posting the second diagram Rob. It makes more sense now but I'm still wondering where I would mount the extra relay on my '88 and I would probably not include the highway/urban switch as it's just something else to remember to switch on and off... after all everything else on these cats is auto!

Still leaning towards the diode fix... seems simpler

 

I would like to add diode into new circuit between terminal 85 and 86 of new relay. It supposed to have resistance also but I don't know the value so better to have diode in circuit to protect relay coit than it will keep burning relay coit. Anybody has any ideas, I will be glad to take that.

 

Well, after a couple of days pouring over diagrams and scratching my head the solution was so damn simple I thought I had better post how it is done...

1) follow the instructions on wiring a diode in the middle of a 15cm (about 6inches for our USA Friends) piece of insulated wire and shrink wrap it remembering which end is the cathode (the banded end)

2) strip about 1cm (1/2 inch) of insulation from each end of the wire ready for connection and fan each end of copper slightly as opposed to twisting it

3) remove the cooling fan relay from it's cradle (on top of the radiator support on the right hand side), identify Pin 86, push the cathode end of the fanned wire into the slot where Pin 86 sits and then reattach the relay (the pin of the relay will lock the wire in place)

4) remove the air con clutch relay (diagonally opposite the cooling fan relay in the same cluster) and identify pin 87... push the non-cathode end of the fanned wire into the slot where Pin 87 sits and then as before, reattach the relay, locking the wire in place.

5) Test as described and then sit back and enjoy the fact that the cooling fan will now operate when your air con is turned on!

I don't think I can make it any simpler than that....

 

Jagfix38,

That's too simple. Not that I would know what to do, but it's just too simple. I wouldn't even need a picture book with these instructions.... I cant' handle that!

Have you done this procedure yet?

 

Yep... all done and working correctly. It took me 5 minutes to solder up the diode and less than 5 minutes to wire it in and test it... no cutting into or splicing original wiring and it can be easily removed if you need to.

ps.. the diode was $1 and the wire and solder I had laying around. Would have to be the least expensive repair i have ever done!