Jaguar XJ-S. Manual - part 124

 
 

491

CLIMATE CONTROL

 

 

PERFORMANCE CHECK:  On max cool, this system should provide air at the center vent in the dash in the upper 
30’s F.  Steve S says, “My '85 XJ-S with R12 achieved 35°F at the vents, at idle, doors open, fan auto, max cool on a 
UK 70°F day after I'd topped if off in July of this year.” 

If your car ain’t getting that cold, it ain’t working right.  There are a few things to check.  First and foremost, while the 
system is trying as hard as it can to cool, check the sight glass at the receiver/dryer along the front edge of the radiator 
upper support rail.  There should be no bubbles visible in the glass -- zero, zip, nada.  If there are any bubbles, the freon 
circuit is undercharged.  See page 512. 

If the charge is OK, other things to look at include the adjustment of the linkages on the Delanair MkII system (see 
page 533) and checking for leakage through the heater valve when closed (see page 493). 

 

SYSTEM TYPES:  From the inception of the Jaguar XJ-S until 1987, a climate control system known as the Delanair 
MkII was used.  In 1987, the Delanair MkIII was introduced, and continued in use until the XJ-S ceased production.  
The housing within the dash was a sheet metal assembly painted gloss black in the MkII, while the MkIII is largely 
plastic.  The MkII is controlled by a single servo assembly via a conglomeration of linkages within the right side of the 
console, while the MkIII uses multiple local servos and controls.  Both systems underwent several detail changes over 
their production lives. 

The compressor and freon circuit is essentially common to both systems, as are a few other things.  Within the dash, 
however, the two systems are totally different.  So, the climate control tips are divided into three sections: Things that 
are common to all systems, things that pertain to the MkII only, and things that pertain to the MkIII only. 

Was there a MkI?  Yes, but it was used in SI XJ6 and XJ12 saloons only; it had been superceded by the MkII prior to 
the introduction of the XJ-S.  Hence, it will not be addressed in this book.  Mike Morrin says, “The Mk1 system did not 
have an electronic amplifier and servo, and relied on a thermostatic bellows controlling a set of vacuum valves for 
temperature and air flow control.”  It also had considerably less cooling capacity. 

The 1995-on XJ12’s, which are based on the X300 body, use the climate control system that was introduced with that 
body.  It’s not Delanair.  Obviously, it likewise is not covered in this book.  It has an electrically-operated heater control 
valve, as opposed to the vacuum-operated valve used in the XJ-S.  It also features an electric pump in the heater line. 

 

POLLEN FILTERS:  Richard Mansell reports:  “If you are interested you can get pollen filters for the ventilation 
system.  I have no idea how or where you fit them but according to a Jaguar accessories brochure from 1997 three 
are available: 

 93.5-96 

JLM11696 

 92-93 

JLM11355 

 Pre-92 

JLM11108 

One might expect that these pollen filters would only fit the Delanair MkIII system, so that “Pre-92” probably really 
means 87-92.  If you have an older car, at least ask first before spending the money. 

 

Common Features 

 

 
 

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WINDSHIELD FOGGING:  If your windshield fogs up more than it should, the first thing to do is determine if the 
fogging is on the inside or the outside -- wipe your finger on it, or turn on the wipers.  If it’s on the outside, the problem 
is that your air conditioner is pumping very cold air through the defroster vents, chilling the glass and causing 
condensation on the outside.  There are two common causes for this malady:   

First, the flap that is supposed to close off the defroster vents is not closing properly, or the sealing foam on the surface 
of the vent has rotted away.  In the MkII system in the XJ-S, the flap is operated by a vacuum capsule immediately to 
the right of the center facia vent, but it’s really difficult to get to without pulling the dash (note that the MkII system in 
the saloon is different in this respect, having a vacuum capsule on each side).  The flap itself is basically impossible to 
work on without a total disassembly of the dash, including purging the freon system and pulling out the entire A/C 
assembly.  Sometimes the problem is the hinge the flap moves on, a cheap plastic item that should be replaced with 
something more substantial if you ever have the opportunity. 

Fortunately, the second cause is more common (on the MkII, anyway): the linkage controlling the entire A/C system is 
misadjusted, causing the air coming through the upper half of the system to be colder than it should be.  Readjust the 
control linkage as described on page 533. 

If the fog is on the inside of the windshield, it is usually due to one of two causes: either the condensate drains are 
plugged up causing the system to fill with water, or the heater core has sprung a leak.  To determine which, John Shuck 
sends this tip:  “This sounds crude, but wet your finger and touch the window.  Taste your finger now.  If it tastes 
sweet, that’s antifreeze that’s coming from guess where....heater core.” 

 

CONDENSATE DRAINS:  All air conditioning systems must have a condensate drain to drain the water that 
condenses when the air is cooled.  The XJ-S has two -- small plastic tubes protruding downward and ending well above 
the exhaust system on either side of the transmission.  When working properly, these tubes will be dripping water on 
the exhaust pipes during muggy weather.  However, when the lines plug up, the water fills up inside the A/C system, 
causing wet spots on the carpet, reduced airflow, etc.  It will sometimes dump water on the driver’s or passenger’s feet 
when cornering.  It also appears to be the culprit in a strong tendency to fog up the windshield immediately upon 
starting the car after it was recently shut off. 

From under the car, run a piece of stiff wire up through each of the tubes until it goes all the way into the A/C unit.  
Compressed air might also work.  Since Jaguar made these tubes entirely too small (they are twice this diameter on 
most cars) they get plugged easily and need to be opened up regularly. 

If your drains are plugged beyond this simple repair, Hunt Dabney provides a description of more serious work:  
“Remove the side panels from either side of the transmission tunnel (the ones that have the vents in them).  On the left 
side, if you look at the front-most ‘corner’, all the way to the left when viewed from the side, you should see a rubber 
reducing nipple attached to the lower portion of the compartment containing the A/C coils.  This has a piece of 3/8” 
poly tubing protruding from the bottom, down and through a grommet which passes through the top of the transmission 
tunnel.  This one is easy to get to and remove.  To replace, use new hose clamps, and possibly silicone seal if the 
grommet has problems (or a new grommet). 

“Above this point is a duct, about 4” in diameter and which extends under the dash from the heater a/c unit to the left 
side dash vents.  By rotating the end a bit ccw, it may be withdrawn from the heater box.  This will allow you to look in 
the box and inspect for dust and debris.  Clean out through here if you can. 

“The right side is very similar, but the A/C servo linkages may get in the way and require removal. In fact, it may be 
necessary to remove the servo unit.  Getting in through the duct, as previously described, is workable, but you have to 
remove the glove box.” 

According to Larry Lee, the drains may be getting plugged with bits of the foam insulation used in the system; being 
British non-metallic material, it rots and falls into the drains.  The insulation itself is not worth replacing unless you’re 
doing other major work, because it requires tearing the dash and A/C system apart. 

Note that Technical Service Bulletin #8218 describes a problem with the condensate drains after the airbags were 
introduced in 1989 and up to VIN 165565.  Apparently a revision of the A/C system was necessary, and as a result 

 
 

493

excess sealant on the drain separator plate may plug the drains.  After VIN 165565, the sealing was omitted.  Later, 
after VIN 168340, an additional hole was provided in the separator plate. 

 

PLUGGED CONDENSATE DRAINS -- PREVENTING SECONDARY DAMAGE:  Hunt Dabney says, “Last time 
the drain tubes clogged up on mine, it dumped quite a bit of water over the servo and ruined the feedback pot.  I made a 
mylar shield to prevent this from happening again.  I took a sheet of 6mil mylar (used to use for PC board layout before 
CAD), cut it so that it would fold over the servo assy from the mounting surface side, with tabs folding over the corners 
and openings where required to clear the operating levers, cable and tubing.  Then, crease the folds, install over the 
servo and reinstall the servo cover.  I cut an opening where the foam "friction" piece that pads between the servo and 
the mounting surface go, so that it would not slide due to the mylar.” 

See also the note on the official Jaguar protection for the stereo on page 662. 

 

HEATER CONTROL VALVE:  The Jaguar heater control valve is a vacuum-operated pot metal contraption located in 
the dead center of the firewall, under the rear loop of the fuel rail.  It consists of a metal cylinder with a hole through it 
within a ported housing; the cylinder is rotated to align the hole with the ports to allow flow, and rotated so the ports 
face the blank sides of the cylinder for shutoff.  This valve is expensive, difficult to get at, and prone to corrosion and 
seizing. 

Note that a heater valve should provide a total 100% shutoff of water when vacuum is applied; if it is leaking when 
closed, even slightly, it introduces quite a lot of heat into the climate control system when it is supposed to be in full 
cool mode.  While the supply air from the vents may still seem cool thanks to the operation of the flaps bypassing the 
heater core, the system won’t work as efficiently as it should.  When in doubt, test it; connect the valve to a 5/8” garden 
hose with a hose clamp, turn on the water faucet, and suck on the vacuum line with your mouth.  If the flow doesn’t 
completely shut off, you need a new valve. 

It’s a fairly simple matter to remove the intake manifold crossover pipe, and doing so may provide vastly improved 
access.  On the ’83 XJ-S, the mount bracket is held to the firewall with two bolts that thread into nuts welded onto the 
firewall.  However, Michael Bain reports that some models use nylon nuts within the wiper motor area.  In this case, it 
may be easier to remove the intake grille/wiper motor assembly and unbolt the heater control valve from the back side, 
but if the nuts aren’t nylon you won’t get anywhere going that route. 

Do not simply eliminate the valve and plug the hoses.  The hot water supply is necessary for proper operation of the 
climate control system, even when it’s in cooling mode.  A temperature sensor in the heater core will limit the blower 
operation if the water isn’t warm enough. 

When the Jaguar valve causes problems, whatever you do, don’t replace it with another valve just like it!  That metal 
thing is junk.  A better option is to go into an auto parts store and ask for a heater valve for a Jaguar.  Some stores may 
stock the original, but most places -- notably the cheaper places -- will hand you a generic heater valve such as one 
made by Factory Air, part no. 74803.  This valve is made almost entirely of plastic, and costs only about $10.  Although 
some people don’t like plastic, the design of this valve is so superior that it is undoubtedly the most reliable choice.  
This is a domed poppet valve rather than a rotating-cylinder valve, so the reliability of a total shutoff when closed is 
much better.  Discount Auto Parts and Pep Boys sell this valve, and they always seem to have it in stock. 

Note that any vacuum-operated heater valve with 5/8” fittings that is open when there is no vacuum applied will work.  
This valve does not throttle; it is strictly on or off, and the temperature modulation is controlled with flaps inside the 
car. 

Note that the vacuum hose in the XJ-S is 1/8” while the connection on the Factory Air valve is 1/4”.  You will probably 
not want to try to stretch a 1/8” vacuum hose over a 1/4” connection, so plan accordingly and buy an adaptor and a 
short piece of 1/4” vacuum hose while you’re in the store. 

Also note that the plastic valve is so lightweight there is no need to mount it; it can be merely suspended in the hoses.  
Take advantage of this fact and relocate it towards the passenger’s side of the engine compartment rather than trying to 
put it anywhere near where the original was.  This will require some 5/8” heater hose and clamps, and perhaps a “hose 

 
 

494

repair kit” for joining two hoses together, so pick all this stuff up while you’re at the store as well.  Note that, in 
addition to straight 5/8” heater hose, most auto parts stores have a large selection of “molded hoses”, 5/8” hoses with 
sharp bends and curves formed in them.  You might consider choosing a couple of these and using them to make your 
heater valve relocation look more professional. 

Getting to the OEM valve is a pain -- so Peyton Gill came up with another idea: abandon it in place.  As long as it 
doesn’t leak externally (they usually don’t) and it’s not stuck shut (they usually aren’t) then simply disconnect the 
vacuum line (leaving it open all the time), cut the heater hose somewhere over near the right side, install a new valve, 
and connect the vacuum line to it. 

 

BLOWER FANS:  The XJ-S uses two fans, one on each side.  Therefore, there is one more failure mode possible than 
on other cars.  If your A/C is putting out cold air but doesn’t seem able to cool the car, check that both fans are 
working.  If one runs and the other doesn’t, the system appears to be working but capacity is severely reduced.  Since 
both fans feed a common plenum, failure of one fan reduces airflow at all outlets but does not affect one outlet more 
than another.  When both fans are working, airflow is quite forceful indeed at high speed, and cooling should be more 
than adequate. 

The blower assemblies are different between the earlier system and the Delanaire MkIII, but they are similar enough 
that the discussions in the next few paragraphs apply to either. 

 

BLOWER MOTORS DISCONNECTED:  The wires to the blower motors go through a grommet into the blower 
housing and then attach to the motor itself with spade connectors.  Duncan Smith had troubles here:  “The +12V spade 
connector had detached from the post on the motor due to the wiring harness being too tight.  Fix: unbind the harness, 
pull the connector through further until there was a bit of slack and rebind.” 

 

BLOWER FANS - REMOVAL:  The blower housings are outboard toward either side of the car and connected to the 
center core with flexible rubber ducts.  To remove each blower assembly requires removal of the underscuttle cover, 
fusebox, a couple wires, one vacuum line and two bolts. 

In the Jaguar repair manual, one step in removing the blowers is to open the recirculation door and block it open.  The 
next step listed is to remove the bolts holding the blower in.  Please do not infer from this sequence that the blower 
retaining bolts are within the recirculation door; the door must be blocked open simply because it is linked to the 
outdoor air intake, which must be closed to prevent hanging up while the fan is being removed.  The blower retaining 
bolts are on the outside of the housing and are obvious.  Both steps are necessary but unrelated. 

Duncan Smith says, “Clothes pegs are perfect for holding the lower door open.” 

 

BLOWER FANS - MAINTENANCE & REPAIR:  Take the blower assembly out (it’s easy), then take it apart to get 
the blower out (also easy) and remove the impeller from the motor shaft.  Look at the motor and see if there’s any 
obvious damage, like wires hanging out, burnt windings, foreign object damage, etc. 

The blower motors are not overhaulable.  The motor itself is held together by peening over some tangs, and 
reassembling would be difficult.  However, it is possible to repair many problems the motor might encounter.   

Since the British engineers saw fit to make these completely open motors exposed to whatever dust and debris comes 
through the ventilation system, it may be helpful to remove lint and foreign objects from the inner workings of the 
motors. 

Since the bearings are exposed as well, some fresh lubrication will be welcome, but don’t over-oil the rear bearing; 
excess oil may find its way onto the commutator, gumming up the works.  Use a light machine oil, like sewing machine 
oil. 

If the motor looks OK but is seized, force it -- whattaya got to lose?