AC fuse keeps blowing on 93.5 v12 : AC clutch or?


I’m out of ideas with the AC on my 93.5 coupe : the AC clutch fuse keeps blowing, cutting the AC
the car is a 1993 V12 6.0L, with the Sanden compressor

the problem occurred a few times during the first years, but now the fuse blows almost immediately

I used a thermal fuse to replace the standard fuse, so I can diagnose the problem

  • when the AC compressor is running the AC works , makes some cold

  • when the AC clutch relay is activated, I measured 12A goping through, so it doenst look like a short to ground

  • the fuse is shared between AC clutch and air pump, and the air pump clutch seems ok : I took its relay out, and the fuse kept blowing, while the fuse is fine when taking the AC clutch relay out

I searched the forum for ideas, and couldn’t find anything similar

  • is it correct that the AC clutch coil should measure about 4 ohms ? pulling 12A would be like 1 ohm resistance , while I reckon a short in the clutch coil should make it 0

  • can I disconnect the said coil to isolate it from the rest of the circuit and measure it ? How can I disconnect the coil connexion ? I see the insulation over the wiring, but cant be sure there’s a spade connector under it (and I don’t want to damage the AC coil)

  • is iut possible to change the AC compressor clutch with the compressonr on the car ? or do I need to take the compressor off to be able to remove the clutch ?

  • any idea of anyhting which could explain de bloaw fuse ?

thanks in advace

(Richard Dowling, 1979 XJ-S HE+5sp coupe, 1989 XJ-SC, 2003 XJ8 3.5L) #2

My Sanden coil is around 3 to 4 ohms, using a cheap auto ranging DMM.
How I hate auto ranging when trying to measure resistance, dumbest idea ever to autorange resistance measurement.

Sounds like you have a dud coil or a short/partial short in the wiring.
Worth checking the wiring very carefully before tackling the coil.

You can get a Sanden " SD Compressor Service Manual " in .pdf format on line, just Google for it. Best to have a copy of that.

You can take the coil out with the compressor still on the car.
I have changed coils with a compressor on the bench.
Sanden have a rage of special tools but if you have a good selection of DIY tools you should be able to do it. Depends on how easy it is to get access.

(Kirbert - author of the Book, former owner of an '83 XJ-S H.E.) #3

What’s the fuse rating?


fuse is rated 5 Amps, and gets some black marks neat the fuse wire when it blows

@ Richard
thanks for confirming the value I found 4 ohms with a basic multimeter, bur could not get a proper reading with my milli ohmmeter

do you remember if the coil connection is a spade connector, or welded ?

I found the Sanden manual , and check again the wiring : I’m almost sure it has already been changed as the wiring colours don’t match the ones on the schematics (all red instead of red/brown and black)

(Kirbert - author of the Book, former owner of an '83 XJ-S H.E.) #5

If it’s pulling 12 amps and the fuse is rated at 5, I think we’ve found your problem.


I came to the same conclusion , but was surprised by the limited current rush : I thought about a short in the wiring, and this would pull more amps, the partial short in the clutch makes more sense, as according to the Sanden manual, the clutch current draw is between 3.6 to 4.2 amps


I got to disconnect the clutch coil and bingo : the resistance is only 1.5 ohms, so the culprit is there (at least one of them)

access is poor to none, so I reckon I’ll need to get the compressor out to change the clutch coil

  • am I correct about the need to take the compressor out ?

  • I didn’t find the coil alone as a replacement part : I hope I don’t have to change the compressor as a whole. are there some alternative sources ? I 'm sure there are many other cars using the same compressor but the connector could be different

(Kirbert - author of the Book, former owner of an '83 XJ-S H.E.) #8

I know the coil is available separately for the A-6 compressor, but I dunno about the Sanden. It’s very popular so you’d presume it has similar support.

A quick Google search yields hits, but I dunno the particulars of our Sanden compressor. Here’s a sample:

And who cares about the connector? That’s easily rectified if the rest of the coil is correct.

(Richard Dowling, 1979 XJ-S HE+5sp coupe, 1989 XJ-SC, 2003 XJ8 3.5L) #9

On the V12 the Sanden sits in the vee, so with luck you can take out the bolts and lift it up as far as the hoses allow you.
To make life easier you can also detach the bonnet/hood struts and that lets you put the bonnet up vertically on its front hinges. Then you have much better access to the sanden.
Note that there are many Youtube videos dealing with Sanden overhaul.
Worth watching to figure out how to get that pulley off and release the coil.

The coil is a regular spare part, and really only needs one basic design for all the Sanden SD series. Maybe they made a a couple of variations to the coil, but most variations would be the connector to suit different cars.
Like Kirbert said, connector can be cut off and anything you like fitted to the wires.


thanks for the tips
I found a NOS Jaguar part which should be the one I need, but a tad expensive at nearly 300€

I’ll ask for a Sanden replacement part in an AC shop near me , rather than try and get it online , get a wrong one and have to send it back

(Richard Dowling, 1979 XJ-S HE+5sp coupe, 1989 XJ-SC, 2003 XJ8 3.5L) #11

The coils cost maybe US$!0 to US$15 to make.
Expect to pay US$50.
Any local aircon shop should have a suitable one.

(Bernard Embden) #12

This might help


@Bernard : thanks, this was my first read on the clutch subject :slight_smile:

@Richard : I’m sure the Jag one is way overpriced, I’d rather pay 50 :wink:
AC wasn’t that common in the 90 in this side of the world, and even now real specialists aren’t easy to find

(Richard Dowling, 1979 XJ-S HE+5sp coupe, 1989 XJ-SC, 2003 XJ8 3.5L) #14

Oh oh. You surely cannot be talking about the United States of America where aircon for cars was most likely invented. So which side of the world are you and your facelift XJ-S located in ?
It is easy to assume most XJ-S forum members are in the U.S.A. because that is generally the case.

It does help to give location since that will often colour the suggestions and advice given. Even in third world markets, which are predominantly hot countries, most cars for the last 20 years would be sold with aircon so there have to be folks around who know how to fix them with varying degrees of expertise.

Bernard: Excellent photo shoot of fixing a GM compressor clutch.
The one we are talking about is a Sanden. When you have a moment perhaps you can get hold of a Sanden and do a photo shoot for that too.

Early Monday morning here. Have the 2003 V8 XJ up on a hoist to change the transmission fluid in the ZF auto box, supposedly not needing changing in the lifetime of the car or gearbox according to Jag/ZF.
The plastic pan is held on with around 2 dozen M6 screws with those small 6 point star recesses. That is a silly choice because those screws are quite long and all show some signs of corrosion. They were all really tight and sure enough one recess chewed up before the screw released.

Fixes with heat or welding a bold head to the screw head are out of the question. The replacement pan and filter kit has a steel pan and regular bolts as in the photo - a product of common sense.
Already got the fluid out, looks like chicken soup.
So much for ZF expertise, why make simple things complicated ?


the auto gearbox “filed for life” is usually only in the car maker manuals, not the box maker : the GM 4L80E also needs oil changes, while the bolts are hidden by the exhaust pipe . One of the bolts broke when I removed the oil pan
I reckon they choose the big flat head because of the soft material : they could add a washer to spread the load, but this saves the risk of dropping one in the box oil

I’m in France, close to Paris, so not the easiest place for mecanics : A/C is now common, but this had not been the case until around 2000

I’ll take some pictures while fixing the Sanden : I’ve been quoted about 1500 for a replacement one , so will definitely try the fix before

(Richard Dowling, 1979 XJ-S HE+5sp coupe, 1989 XJ-SC, 2003 XJ8 3.5L) #16

Paris location will make some difference to replies on this forum, but even close to Paris there are bound to be mechanics who service aircon systems. Sanden is a popular choice for may cars, perhaps more so for U.S. cars and larger cars elsewhere. On Ebay they are way cheaper than the 1500 ( euro ? ) you mention.
Like Bernard explained, the gold standard for fixing things on the front of the V12 is to remove the bonnet. That is quite easy, just make sure to protect paintwork and have a 2nd pair of hands to help detach and refit.
Once you have the full model number of the Sanden and pull off the clutch you should be able to get another from U/K or U.S.A. for US$50 max.

ZF problem fixed. Luckily with plastic pan was able to check on Youtube nothing delicate close to the seized screw. A few sawcuts and holes drilled close to the screw to weaken the plastic, and just ripped the thing off the box. Then a ViceGrip easily got the screw out.

There must be logic in using plastic pans and Torx head screws, but it baffles me. Mention on Youtube those Torx head screws can be a bit corroded and a PIA to remove. Now have steel pan and regular bolts with a touch of antiseize on them.
The plastic pan looks not much lighter than the steel pan. Must be more expensive to make because every one of the 2 dozen screw holes has a precision steel sleeve inserted to prevent the plastic being deformed when screws torqued up.

The ZF plastic pan has the filter built in so you have to scrap the whole thing when you change fluid - and it goes to landfill since not really recyclable.
The steel pan can be reused with a new separate filter, and of course steel is the very easiest thing to recycle at end of life, just a big magnet to pull it out of rubbish.

(equiprx) #17

Let me know if you can’t find replacement bolts or Sanden parts at a reasonable price.
I have lot’s of leftovers from my 94 V12 coupe restoration.
PM me with questions or availability.

(Bernard Embden) #18

Plastic pans are used because they can be manufactured cheaper than steel or aluminum.
I believe that torx head screws are easier for the robots to assemble, as the screws are quite close to the pan sides.


first source for the Jaguar replacement coil was on an outdated web site, so part not available , but I hope I’ve got a real source for the Sanden parts.
They’re asking about the exact type of SD709, or the exact ref of the coil, or even a picture , which is not easy without taking it off : I reckon that’ll be this weekend job

I’ve seen suggestions about taking care of cleaning the condenser and refitting some foam bit to preserve the air flow through the condenser , but when I checked the part list, I couldn’t find any foam part, all are listed for the 5.3L, not the 6.0L : are they the same or not ?

I’ll try and have a look, but they probably have gone to dust

(Steve) #20

You mean radiator, not condenser, right? The latter is much smaller than the former.
The radiator needs all the air routed through the core, and the foam seals the gaps between the radiator and the body.