Jaguar XJ-S. Manual - part 127

 
 

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There is a second type of protection switch available: a pressure-operated switch that supplies a ground to the 
compressor clutch when the freon circuit pressure is normal.  This second type is the best to use; the early system with 
the thermal fuse is temperamental at best.  The pressure switch has a plastic body, as opposed to the thermal type which 
has a metal body with a heat probe protruding into the compressor.  Since the pressure sensor has no protruding probe, 
it can be installed in a replacement compressor in place of the aluminum blank-off plug.  According to Stefan Schulz, 
Jaguars began being fitted with this type from the factory in the mid-80’s. 

Note that the thermal type switch is normally open and connects to ground in the event of trouble, while the pressure 
type is normally connected to ground and opens in the event of trouble.  To use the pressure type protection switch, 
modify the harness so the power goes straight to the clutch and the ground terminal of the clutch is wired to the 
pressure switch; a three-connector fuse is not needed. 

If you live outside the US, the A-6 compressor is anything but cheap.  Someone could make a million buying 
compressors in the US and selling them overseas.  In any event, after paying top Euro or Rasbutnik or whatever for a 
new compressor, you’re not likely to want to forgo the protection circuit -- but it may be difficult to find either type 
sensor or the three-connector fuse.  Mark Barker of the UK found a solution:  “An alternative to factory (one-time 
acting) thermal fuse is to fit a resettable thermal cutout.  It's a small round thing with spade tags and a small red reset 
button.  You glue it (epoxy is fine) to the side of the compressor and it is wired in series with the clutch.  Test the 
wiring by running with one of the spade tags unplugged. 

“In the UK it is available from RS Components (

http://rswww.com

) as stock no. 228-2513 (for a 70°C one) at 3 UKP.” 

 Sean Straw adds, “For worldwide (except USA) affiliates, check out 

 

 

http://www.rs-components.com

 

“They list numbers for offices in different countries.”  Robert Egerton adds, “If you are in the UK the retail outlet of RS 
is called Electromail and you can get them on 01536 294555.” 

Of course, 70°C is too low.  “I found this can trip during a 'pull down' on a hot day.”  Mike Morrin says, “The 
compressor (at least on my car) routinely gets to 85°C.  Everything in the valley is over 75°C on a hot day.”  Barker 
responds, “The sensor is also available as a 90° and higher too, on the same page.  Similar part nos.  What we need to 
sort out now is which of the available trip temperature ones is best to use.” 

Barker adds one last note:  “Note that after I did all this, the air-con chap who gassed my system told me there was a 
retrofit which had high (overload) and low (lost charge) pressure sensors which would be even better; sorry I don't 
know any more about it.” 

If your compressor is simply getting too hot, see the section on high freon pressures on page 514. 

 

AIR CONDITIONER COMPRESSOR CONNECTOR & DIODE:  It would be helpful to have a diode wired into the 
compressor clutch connector; see the discussion on inductive loads on page 557.  Of course, the Jag doesn’t come with 
one.  However, if you go into an auto parts store and ask for the special connector that plugs onto a GM compressor, 
the connector comes with a diode built in.  One such part is made by Conduct-Tite, part number 85143, found in an 
AutoZone; another is made by Factory Air, part number 37201, found in a Discount Auto Parts.  Dennis Kindig, who 
owns an ‘87 XJ6, says, “I used this connector to replace my original wiring when I changed compressors and converted 
from the thermal fuse arrangement to the high-side low pressure switch.” 

Of course, you can accomplish the same objective by simply buying a suitable diode at Radio Shack and adding it in to 
your existing wiring. 

 

AIR CONDITIONER COMPRESSOR FRONT BRACKET - A-6:  The front end of the A/C compressor is supported 
by a plate bolted to the front of the timing cover.  This plate is not symmetrical; it goes in only one way.  If you put it in 
backwards, your compressor pulley won’t line up right with the belt.  The objective of the asymmetry is to position the 
compressor a little to the left of center so that the drain plug on the A-6 doesn’t jam into the A bank head.  The bracket 
at the rear of the compressor is asymmetrical also, but you couldn’t install it backwards if you tried. 

 
 

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AIR CONDITIONER COMPRESSOR - MOVING OUTTA YOUR WAY:  As in most cars, the compressor is 
connected with flexible hoses.  This enables some movement of the compressor for such jobs as replacing the spark 
plugs without disturbing the freon system.  Several people, including Victor Naumann and Harry Trafford, have 
pointed out that a block of wood positioned between the V and the top of the radiator can be very helpful to hold the 
compressor forward and above its normal position while you’re working. 

 

AIR CONDITIONER COMPRESSOR - REMOVAL AND REFITTING - A-6:  In order to correct for tolerance in 
dimensions such as the overall length of the compressor, the holes in the rear compressor support where it is bolted to 
the valley cover are very slightly slotted, so the rear support can be slid back and forth a bit and then the bolts tightened 
down.  So, whenever the compressor is replaced with a different one or the valley cover has been removed, the proper 
way to reassemble would be to leave these two bolts loose until the compressor is in place and the bolts at the back end 
and all four bolts in the front support plate are tight, then tighten the two bolts holding the bracket to the valley cover 
last. 

When you are not fiddling with the valley cover bolts or replacing the compressor with a different one, lifting and 
reinstalling the compressor without loosening those bolts seems to work well enough if you do things in the right order. 
 Always loosen the two bolts that attach the front mounting plate to the timing cover before lifting the compressor out.  
During assembly, always have all four bolts at the front (two holding the plate to the timing cover, two holding the 
compressor to the plate) in place but loose while tightening the bolts in the rear support.  Be sure to reconnect the 
ground wire. 

 

COMPRESSOR HOSE CONNECTIONS:  The freon lines connecting to the GM A-6 each have a hexagonal block on 
the end that fits against the rear plate of the compressor.  There is an O-ring in a recess on the back of the compressor 
that this block fits against, and a single bolt between the two ports pulls a 1/4” thick racetrack-shaped bar against the 
back side of the hexagonal blocks to hold them firmly against the O-rings and ensure a seal.  This same bolt also holds 
the bracket that mounts the cruise control actuator. 

That 1/4” thick bar, C36983, sure looks like a sturdy and massive part -- but it’s not.  When this system is worked on, 
more often than not that part is found to be bent in the middle when removed -- and of course the mechanic turns it over 
so it gets bent back the other way when reinstalled.  People leaning over the engine compartment to work on the water 
pump, etc., and pushing on the hoses apply a terrific amount of leverage towards tilting those hexagonal blocks and 
breaking the O-ring seal underneath. 

Why would GM design something so prone to leakage?  Well, perhaps it was a mistake -- but it was a mistake they 
corrected.  Later GM cars don’t used these two separate blocks with a 1/4” plate holding them in place.  Instead, they 
make both connectors into one large connector about an inch thick that the bolt holds in place directly.  That way, 
there’s no way it’ll get distorted -- even if made entirely of aluminum, as most later ones are. 

This author relocated the cruise control actuator elsewhere and made a thicker bar to replace the 1/4” thick bar.  There’s 
no need for the racetrack shape; simply take a piece of 1-1/2” x 1/2” steel bar, cut a 3” piece off, and drill a 3/8” hole in 
the middle.  With the large flat washer and the cruise control bracket omitted, the original bolt was the correct length to 
hold this thicker bar.  And there’s not a chance in hell it’ll bend; you can feel the difference just tightening it up. 

If you are not relocating the cruise control, it still might be a good idea to fab a thicker bar for this retention.  The entire 
cruise control actuator will be relocated rearward by the amount of additional thickness in this bar, so if you go with 
1/2” as I did the actuator will be positioned 1/4” farther rearward than before.  Check carefully to make sure it all fits 
without running into the distributor cap, as taking that bar back out entails discharging the freon circuit.  You probably 
should also provide a bolt that’s longer by 1/4” so you’re not relying on too few threads in the back of the compressor.  
An even better idea would be to replace that bolt with a stud; seat the stud fully, then hold the plate in place with a nut. 

 
 

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An alternative idea might be to purchase a second 1/4” thick bar C36983 -- or make one.  Then install the two bars with 
the cruise control actuator bracket sandwiched in between, which will hold it in exactly the same place as before.  
Again, you’ll need a longer bolt. 

 

AIR CONDITIONER COMPRESSOR OIL CHARGE:  Section 82.10.14 of the ROM explains how to deal with a 
compressor delivered with oil in it.  However, a typical rebuilt compressor will nowadays be delivered without oil since 
there are three different types of oil (mineral, ester, or PAG) that you may end up using.  Read the tag on the rebuilt 
compressor. 

If it is dry, follow the directions in steps 12-15 of Section 82.10.20 -- but note there’s an error there.  In step 15, it twice 
refers to the amount of oil removed in step 14.  It should refer to the amount of oil removed in step 13 both times; that’s 
why you were measuring in step 13. 

These directions -- as well as the directions that come with the new compressor -- involve draining the oil out of the old 
compressor to measure how much was in it.  Nowhere does it provide any clue how to drain the oil out of the old 
compressor -- or from which opening.  James Teston says it’s really all openings:  “Pull the compressor off, keep it 
horizontal, and drain the oil you have in it out from the drain plug on the bottom of the sump.  Then flip it vertical and 
drain it from the pressure and suction ports.  Then put it any which way and rotate the clutch quickly to blow out 
whatever oil might be left.” 

They also tell you to add a similar amount of oil back into the new compressor, again with no clue on how to 
accomplish this.  If you don’t do it right, you may end up with oil all over the place -- and no idea how much is in and 
how much is all over, which would be bad.  This author recommends the following:  Add no more than three or four 
ounces to the compressor while it’s on the bench.  This may be added through the drain plug or it may be added into the 
suction port while turning the hub of the compressor to suck it in -- but don’t turn it more than about one full turn or 
it’ll start pumping it back out the pressure port.  Put the caps back on the ports, or go ahead and connect the hoses and 
cap the ends of them.  If time permits, leave the compressor sitting nose-down for a while so the oil can collect around 
the front seal.  Install the compressor.  If you need to add more oil, disconnect the suction hose from the fuel cooler, 
hold this end upward and pour the oil into that end of the hose.  Turn the compressor by hand to get this oil into the 
compressor. 

Teston points out that, since the oil circulates around the system, as long as you have some in the compressor when you 
start it up you can add oil pretty much anywhere.  “The A6 has a sump, so the correct amount of oil will eventually find 
its way into it if you can't fill it all at once.  Just add some to each section as you put them back together.  Don't dump 
any directly in front of the expansion valve or put a large slug in the bottom of the condenser.” 

Finally, just before startup be sure to turn the compressor over by hand a dozen or more full turns to make sure it’s not 
liquid-slugged with oil. 

 

FITTINGS:  When buttoning up parts of the freon circuit, please remember that the sealing of these connections does 
not depend on getting the nut tight enough.  As parts are assembled, an O-ring is compressed between the OD of the 
tube and the ID of the fitting, and it’s this compression that provides the seal, not the tightness of the nut.  The nut 
merely keeps the assembly from rattling or blowing apart.  Just tighten it down snugly and quit; there’s no need to be 
grunting on it and many good reasons not to be grunting on it. 

 

PLUMBING -- EARLY CARS:  Bernard Embden says, “The fuel cooler on the air cleaner is standard equipment on 
the post-H.E.'s I believe.  Coventry West said that original A/C parts for the pre-H.E.'s were no longer available. Not 
wanting to have hoses made up, I just scrapped my A/C system altogether and went with the hoses/fuel cooler etc. from 
the 1988 model.” 

In this day and age, it perhaps wouldn’t make sense to update to the hoses from the 1988 model which was also 
originally fitted with R-12.  A better idea would be to have the original hoses rebuilt with barrier hoses as described on 
page 520. 

 
 

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FILTER/DRYER:  The flow through the dryer is from left to right in the XJ-S.  Be sure to install the replacement dryer 
in the correct direction; they always have flow direction arrows on them.  Do not simply install the new dryer so the 
sight glass is in the same place as it was on the old one; the sight glass may be on either the inlet or outlet end of the 
dryer. 

 

EXPANSION VALVE:  The expansion valve on this system (at least on the ’83) is fairly standard; if you look through 
an A/C shop’s parts book you will find there are several interchangeable part numbers, including some from Japanese 
cars.  But further, there are several other part numbers that represent similar expansion valves except that the capillary 
tube and/or sensor tube are different lengths.  The expansion valve called out for the XJ-S has very short tubes, since 
the places they go are only a couple inches away.  But it still may be beneficial to get an expansion valve with longer 
tubes just to make it easier to install. 

Also, some of the expansion valves have the capillary tube attached on different sides or at different angles.  Selecting 
the optimum arrangement here can also ease installation considerably. 

The expansion valve may be a common configuration, but it’s certainly no fun to get at.  I will provide a few tips that 
hopefully will be of some help.  Obviously, don’t even consider this job without removing the balance pipe between 
intake manifolds first.  If you still have a heater valve in its original location, you might choose to remove it -- and don’t 
put it back, install the generic version elsewhere instead as described on page 493.  Remove the hose that goes to the 
fuel cooler, both to get it out of the way and to install a new O-ring in it while you’re here; advice on removing it is 
under “Hose Removal” below. 

The body of the expansion valve is L-shaped and has male threads on both ends.  Hence, the line going into the 
evaporator behind the firewall has a trapped nut on it.  The hex on this trapped nut is 7/8”.  To get this nut loose, you’ll 
be having fun just finding a wrench to get on it.  Chuck Sparks suggests an offset box end with a bit of the box cut out 
to make it look like a flare nut wrench; slip it over the body of the expansion valve itself, then slide it rearward onto the 
nut.  It’s possible to do it with other tools, but this is perhaps the slickest way. 

You’ll also need a wrench that fits the body of the expansion valve itself.  There’s a hex on it, but for some reason it 
doesn’t seem to be any standard size.  You probably can’t get a monkey wrench on it, so the wrench to use is either a 
5/8” or 16mm open end.  It’s a bit loose, but it’ll work. 

To break the nut loose, Sparks suggests you disconnect all the other lines to the expansion valve first.  Then put your 
modified offset box end wrench onto the nut and turn it to the right (facing the firewall) just enough to take up the 
slack.  Then, using the 5/8” or 16mm wrench, turn the expansion valve itself to the left.  This way, Sparks argues, 
you’ll have less chance of damaging the line on the evaporator -- which would be seriously bad. 

The nut on the tube coming down on top of the expansion valve requires a 3/4” or 19mm wrench.  A crowfoot works 
great here.  If it’s really tight, be sure to hold the body of the expansion valve; don’t just break the tube off the 
evaporator.  Some expansion valves have a hex below the threads, others have only two flats parallel to the sides of the 
valve body; either way, it’ll be a 1/2” that fits.  If you can’t get a wrench on it, perhaps you’d be well advised to grip the 
body with a pair of vicegrips or some such, destroying it if necessary -- you’re taking it out, and you won’t be reusing 
it.  Far better to ruin a scrap expansion valve than your evaporator.  And you won’t have a problem putting the new 
expansion valve in, because there’s no need to get that nut that tight. 

The nut attaching one sense tube to the return line requires a 9/16” wrench -- but you knew that already from checking 
the one on the replacement expansion valve. 

The other sense tube has a little coil on the end that must be installed against the pipe coming out of the evaporator, and 
it must have some insulation put over it so that it senses the temperature of that pipe and not the surrounding air.  On 
most cars, this coil is merely strapped to the pipe with a tar-like stuff.  However, on the XJ-S there is actually a little 
boss built onto the evaporator outlet fitting just for this coil.  Once you get the old tar stuff off, you must loosen two 
Pozidriv screws to get the old coil to slide out.  Fortunately, this clevis is positioned horizontally so the screw heads 
face straight up, making it a fairly reasonable job to get a screwdriver on it.