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Air Conditioner/Heater

  Experience in a Book
Air Conditioner/Heater



SYSTEM TYPES: Despite many minor revisions, the basic air conditioning and heating system in the XJ-S remained essentially unchanged until 1987. In 1987, the entire interior system was replaced with a new design, commonly referred to as the Delanair MkIII. The earlier unit within the dash was a sheet metal assembly painted with gloss black paint, while the later system is largely plastic. The earlier unit was controlled by a single servo assembly via a conglomeration of linkages within the right side of the console, while the Delanair uses multiple local servos and controls.

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 following discussion is divided into three sections: Things that are common to all systems, things that pertain to the pre-1987 system only, and things that pertain to the Delanair MkIII system only.


Common Features


AIR CONDITIONER COMPRESSOR: Up through 1992, the Jaguar A/C compressor was labelled "Harrison" but was in fact the standard GM item referred to as an A-6 -- and therefore comparatively cheap to replace. In fact, it is generally recommended to simply replace the compressor rather than attempt even the simplest repairs. After a few years, the O-rings start to fail, and each time you correct a leak you must have the system evacuated and recharged. With the current regulations on R-12 refrigerant, the cost of a single charge can exceed the cost of the compressor. If you are having the system recharged anyway and the compressor is more than seven or eight years old, it might be wise to simply replace it even when it is still working fine.

Although you can find an A-6 compressor really cheap, Randy Wilson says, "The compressors should be good for many years. Continuous failures are not the fault of them being rebuilt units. It's the fault of them being cheap quasi-rebuilt units. This is a fairly major problem we fight in the auto industry.

"I can buy these A-6 compressors from a local distributor for $49 per unit in very small lots... with no core return. These units, I can tell you from experience, have an average life expectancy of around a month. Many fail the first day. I have found a rebuilt compressor that I like. It's a lot more expensive. But I haven't had one of them fail yet."

The threads on the replacement compressor are likely to differ, in which case you will have to replace the mounting bolts. In particular, the two mounting bolts at the bottom rear and the long bolt that holds the inlet and outlet connections in place are 10mm on the original, and will probably have to be replaced with 3/8" bolts (either fine or coarse, they vary) when installing a replacement. 3/8" is only slightly smaller than 10mm, so sleeving will not be necessary. Also, the small front mounting bolts as well as the bolt that holds the fuse assembly may have to be replaced.

The new A-6 compressor also may not fit the protection switch that was in the original compressor. Read the section below.

From 1993 on, a Sanden (Japanese) compressor was used. While many may bemoan the discontinuation of the excellent A-6, the Sanden likewise has an excellent reputation among A/C mechanics.


COMPRESSOR PROTECTION CIRCUIT -- A-6: Just below the inlet and outlet connections on the A-6 compressor is a sensor held in place with a C-clip, with a wire connected to it. On the 1983 XJ-S, this is a thermally-operated switch that shorts to ground in the event that there is trouble with the freon system. The shorting causes a resistor within a three-connector fuse assembly to heat up, which in turn causes a fuse to melt, breaking power to the clutch and disengaging the compressor. This is a common arrangement on GM vehicles, and the fuse assembly is readily available. The fuse is usually attached to a mounting hole on the compressor itself.

Do not connect the fuse backwards. There is a little tang on the center connector that is intended to indicate which way the plug goes, but it's not very foolproof. If you install it backwards, the clutch will not engage and the fuse will blow immediately.

A replacement compressor is likely to have an aluminum blank-off plug in place of the fault sensor. It is probable that you cannot install the thermal type sensor in place of the plug because there has to be a suitable opening underneath the plug for the tip of the sensor, and there often isn't. However, the sensor wire can just be left disconnected and the system will work fine -- there just won't be any protection for the compressor if the system loses freon. In fact, it is just as well to remove the fuse assembly as well and run the power wire directly to the compressor clutch. Since the standard procedure is to replace the compressor in the event of freon loss anyway, this may be acceptable.

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.


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. To be safe, mark the plate before removal.


AIR CONDITIONER COMPRESSOR -- MOVING OUTTA YOUR WAY: Many jobs, such as changing spark plugs or pulling the cam covers, requires moving the compressor a little bit without removing it entirely or disconnecting the freon lines. 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.

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.


FILTER/DRYER: Apparently, the receiver drier unit on some Jags has O-ring fittings; on other Jags, the unit has flared fittings on it. Either drier should be readily available, it is not a special Jaguar part. Be sure to install the replacement in the correct direction (they always have flow direction arrows on them); the location of the sight glass may not be a good indicator, since there are reports of the sight glass being on either the left or right side.


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 Jap 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 sensor tube has a little coil on the end that must be installed against the pipe coming out of the evaporator, and must have some insulation put over it, so that it senses the temperature of that pipe. 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 Phillips screws to get the old coil to slide out.


REFRIGERANT LEAKS: Michael Minglin says, "A possible solution is a refrigerant additive available from Cryo-Chem Int'l at 1-800-237-4001. It is called Cryo-Silane and reportedly seals small refrigerant leaks, without clogging the system. It is guaranteed to seal and hold for one year any a/c system that takes longer than six hours to leak down. As I said I have not yet tried it, and it isn't cheap, but this may be the answer to small hard to find leaks.

"On the matter of hard to find leaks, with the a/c service gauges hooked up it is impossible to find leaks in the service ports or valves. If your mechanic cannot clearly show you the leak, have him disconnect his service gauges and check the the service port valves before starting to change out expensive hoses and parts."


LEAKY SCHRADER VALVES: The guy who works on my A/C for me has a tool for replacing the Schrader valve without discharging the system! It screws onto the fitting, then allows you to unscrew the valve from the fitting within a glass housing so nothing leaks out. Put a new valve in, problem solved. Only a little squirt of freon is lost when you remove the tool, the amount that filled the volume of the tool itself.


FREON REPLACEMENT: R-12 is soon to be history, and many XJ-S owners are concerned about what they will have to do when they can no longer get their freon circuit recharged.

One possibility, and the first to be "approved", is to modify the system to use R-134a refrigerant. Jaguar offers a retrofit kit; the part number is JLM 11610 for the 1993-94 XJ-S with a Sanden 709 compressor, and JLM 11611 for the 1979-92 cars with the Harrison compressor. To quote from Technical Service Bulletin #8239: "The primary changes involve the replacement of the existing compressor lubricating oil with an oil compatible with both HFC R-134a refrigerant and with the residual R-12 lubricating oil. It is not possible to completely flush R-12 type lubricating oil from the refrigerant system prior to changing to Ester oil and R-134a. Additionally it is necessary to replace the input shaft seal of the compressor with a seal compatible with the R-134a refrigerant and oil." Note that the use of R-134a refrigerant reduces the cooling capability of the system somewhat.

Perhaps a better choice is R-406a, which has now been approved for automotive use. More expensive than R-134a, but is not only a drop-in replacement for R-12, it also increases the capacity of the system by a few percent. There is more info available on the WWW at and any search of the WWW is likely to turn up a flurry of information on R-12 substitutes. Or call McMullen Oil at 1-800-669-5730 or Monroe Air Tech at 1-800-424-3836.

Other possibilities include a host of up-and-coming substitute refrigerants such as Hot-Shot or GHG-X4 (GHG in honor of the chemist who put the formula together, George H. Goble), supposedly direct replacements for R-12 with little or no conversion necessary.

There are also folks who have figured out how to charge the system with a mixture of propane and butane. This is not recommended, however.

Michael Minglin found a page on the WWW "for those of you who would like to be able to purchase R-12, R-134a, or just about any other kind of coolant, to do your own A/C repairs:

"At this website you can download the EPA section 609 manual free, take the test online for under $10, and print out an instant temporary EPA certification certificate, if you pass the test. The actual certification card is mailed in about 30 days."


HOSES: Most A/C shops claim to be able to rebuild hoses. It turns out that some hoses are more difficult to rebuild than others, and the more difficult ones require a special crimp tool that, while reasonably priced as shop tools go (no power, hand operated), was only introduced relatively recently. If the A/C shop is dealing with the older crimp tools, it cannot rebuild some hoses. The usual result is that they will cut the fittings on your old hose and braze on sections of tubing that their tools can fit a hose to. This looks like c__p when done, but does work.

If the fittings on your hoses happen to be aluminum, only the newer tool will work, since brazing is out and the older tool will crush the tube.

Now, does any of this apply to the Jaguar? Well, probably not mine; it appears to have standardized fittings made of steel, so perhaps the older crimp tool will work. But I dunno what fittings are used on other Jaguars, so I thought I should clarify the situation. I have mid-80's Hondas that have unique, aluminum fittings on the hoses; a shop with the new crimp tool can rebuild, a shop without it will tell you that the hose is unrepairable and you must buy a new one from Honda. If the newer Jags have similar developments, take note.


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 major causes here:

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. On the pre-1987 systems, the flap is operated by a vacuum capsule immediately to the left of the glovebox (left hand drive cars), to the right of the center facia vent, but it's really difficult to get to without pulling the dash. 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 pre-1987 system, 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.

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 ëcorner', 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 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.


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. One better option would be to take it to an auto parts shop or auto A/C shop and ask for a Chevy valve that has 5/8" hose connections. The Chevy valve is a butterfly type and is made of plastic and stainless steel, and weighs so little that it doesn't need to be mounted; it can merely be suspended in the hose. It also costs only about $20. Make sure the valve you buy is normally open, and applying vacuum closes it. With a little hose rerouting, one of these valves can be located at the right rear corner of the engine compartment where it's easy to get at.

Unfortunately, the Chevy valves are not that great either; the shaft is stainless but the butterfly itself is rubber over a basic steel disk, and the steel rusts and blisters the rubber off, causing it to leak when shut. Oh, well, at least it's cheap.

A better option yet is to go into an auto parts store and ask for a heater valve for a Jaguar. Some stores will stock the original, but other places -- notably the cheaper places -- will hand you a generic heater valve 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 like the Jaguar original or a butterfly like the Chevy valve, so the reliability of a total shutoff when closed is much better than either. Discount Auto Parts and Pep Boys sell this valve, and they always seem to have it in stock.

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.


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.


VACUUM: The control system relies on a supply of vacuum from the engine, and stored in a reservoir. As Tom Wagner discovered, it pays to make sure the supply is working before troubleshooting the rest of the control system. There is a check valve in the line to allow the reservoir to hold vacuum when the throttle is opened, and this check valve stuck shut -- preventing either the reservoir or the control system from getting any vacuum.


VACUUM CHECK VALVE: One might expect that the normal failure of the vacuum check valve is that it fails open, but Mike Morrin had the opposite problem. "My A/C system has always had marginal performance of the vacuum actuators, with the heater valve (new) and centre vent flaps always slow to operate. I got tired of the centre vent taking 5 to 20 minutes to open.

"Tonight I decided to check the vacuum non-return valve, which seemed to be working. While trying to decide what to do next, I was sucking on the non-return valve, and it occurred to me that I was sucking rather hard before any air got through.

"On impulse I tried to pull the valve apart to see what was inside, but it was too tight (or glued together). I then poked a piece of steel wire in the end where the air goes in, and there was a small click. That must have been the rubber thingy unsticking from its seat, because the valve is now much easier to suck through (but only one way). After refitting, all the vacuum actuators are now working like clockwork.

"That is the easiest repair this week.

"The XJ-S help book mentions that these valves sometimes block up completely, but this was only partial, and seems to have been fixed by a poke in the eye with a blunt stick."


CENTER VENT: The center dash vent on most XJ-S's has three sections: a section on the left and right ends that can be adjusted to aim where desired, and a center section with no adjustability that simply blows straight rearward. Here in Florida where the weather is both hot and humid, this center portion can blow enough cold air straight back to cause the rear windshield to fog up -- which is a real pain, because the rear window defroster has a timer and won't stay on indefinitely, you have to keep turning it on and off to maintain visibility in the mirror! Those who don't have fogging problems still dislike that center vent blowing air to the rear, since only sadists ask anyone to actually sit in that rear seat. Peter Cohen confesses, "Over the years, I have developed the unconscious habit of driving with my elbow resting on the console, arm up, and my hand positioned as a diverter to direct the cool air toward me."

Emile A. Des Roches suggests two possible fixes: "The Cheap Solution -- Lift off the surrounding wood (gently); the plastic vent will come out with gentle even pressure. Cut a piece of relatively stiff black cardboard to the height of the inside (towards inside of dash) vent and to a width roughly 2" narrower than the width of the center vent. Place same (black side facing cockpit) in the vent and reassemble. This solution performs the same function as resting one's hand in the air to divert air towards the driver and is far more sanitary."

This author made a similar modification to his center vent, except he used black plastic instead of cardboard and shaped it into a V so it would more definitely deflect the air to the sides. Using the simple flat piece may cause more blockage rather than deflection -- which may be desirable since it would result in more air flowing out all the other vents.

To all this, Franck Guilloteau adds: "While my car is an '85, the wood trim is in immaculate condition and I found that after several unsuccessful tries it wasn't worth the risk of breaking or chipping the trim. I resorted to an alternative method of removing the two directional vents of the main center vent. A small screwdriver, X-acto blade and minimum dexterity will do the job in five minutes. Directional vents have a small leaf spring that increase the friction and hold them in place; it can be pushed out prior to removing the vent. These openings allowed me to slide black cardboard (or plexiglass covered with black felt in my case) and wedge it in place from behind. All told a really "cool" mod."

Des Roches continues: "The More Problematic Solution -- Replace the center vent with one from a very late XJS. At some point after 1993, the center vent design with moveable vanes at the edges and fixed vents at center was replaced with a design that consists of two (no space between) adjustable vents. This is a direct (no trimming) replacement for the earlier unit which presumably could be obtained from either Jaguar spares or a wrecking yard." Dean Gosselin adds that the part part no. is BEC-26361.

Dan Jensen adds, "I changed out the center vent on my XJ-S... It makes a dramatic difference in the amount of cold air that can be directed over the driver and/or passenger. I would offer one additional note to the installation instructions. While the replacement vent has the same width and height as the original in my car, it was approximately 1/8 in. deeper. The extra depth resulted in the vent face extending out a comparable distance from the metal dashboard and prevented the wood fascia from sitting firmly against the dash. As a result, I had to get out a wood rasp and file off 1/8 in. around the inner perimeter of the vent. This took about 15-20 minutes, including the time needed to get all the little specs of plastic off the louvers when I was finished. In addition, it was necessary to file two small central notches in the metal dash to accommodate two added bulges in the new vent. This took no more than a minute or two with small round file."

Samuel Louw provides an incredibly detailed description of this job, in response to the concerns that many people had about damaging their wood trim: "It is really simple and you don't have to be an engineering genius to be able to do this. The most scary part is actually to remove the wooden center fascia, since this holds the vent in its place. It really sits tight. There are four metal springloaded pins that are attached to the backside of the fascia and are pushed into four holes which are in the metal dash plate behind the nice wooden fascia. When the fascia is replaced, the four metal pins are pushed into their holes and the springloaded clips are compressed, not in the direction of the pushing action but by the sides of the holes, since the clips are V-shaped. Now when you want to remove the fascia, you first have to overcome this spring action. Since you think the fascia is waferthin and will break, you might want to give up, but that piece of wooden fascia is almost 8mm thick in places. You have to open the glove compartment and slide the blade of typically a steel table knife underneath the fascia. Then you must start wedging it away from the dash. The right side steel pins are app 5mm away from the top and bottom of the fascia and app 35mm in from the glove box side from where you will be wedging. The left side bottom pin is also app 35mm from side, but the top pin is app 70mm from the side and in the area where the fascia is only about 13mm wide. Be careful of breaking the wood there. I hope that by knowing beforehand how things look at the back it will make you more comfortable to do the job.

"The new vent has four small plastic flanges with holes in it, two per side along the two long horizontal sides of the vent. The flanges are about 10mm x 10mm. They have to be removed, since the pre-'93 cars do not have holes through which the vent is fixed in position. This is definitely not needed, since the vent is held in position by the center piece of wooden facia, and that really sits tight. So, you have to remove those flanges (can be broken off carefully with normal pair of pliers) and then just file the leftover away.

"The other small job is also due to a small difference on the new vent, but again, this is small and easy to do. The new vent has has two small D-shaped bulges on both sides. This will most probably interfere with the metal plate of the dash where you have to push in the vent. Just mark the position of those bulges and file away the notches in the metal plate (About 5mm wide and 3mm deep and halfround shape; use small round file).

"I did not notice the problem of the new vent being deeper than the original, as was noted by Dan Jensen. Thus I did not have to do that filing to make it less deep. My new vent pushed in all the way until it settled against the rectangular sponge seal and there was no interference with the wooden fascia due to a bit of vent protruding. If you do find this problem, just file away the required amount from the rear of the vent.

"The correct Jaguar part no for the new vent is BEC26361. Do remember to buy the new foam seal as well. You are not likely to save the old seal, as it will have rotted and deformed.

"You will have complete control over the direction of air flow both up and down and to the sides. If you live in an area with hot weather as I do, it is essential. You won't believe the difference."


Pre-1987 System


TRAINING MANUAL: Jaguar, back in the days of British Leyland control, issued a "British Leyland Service Division Dealer Training" manual, "Aid # S1002" on the Environmental Control System. Although it's described as intended for the "Jaguar XJ6, XJ12 Series Two", the same basic system was used in the pre-1987 XJ-S. This book is long out of print, but if you happen to find a dealer or mechanic with one you definitely want to have a copy made.


HEATER CORE REPLACEMENT: The heater core ("heater matrix" for you Brits) on the pre-1987 XJ-S has integral pipes that extend through the firewall, where hoses connect it to the engine cooling system. To get it out intact requires disassembling the entire dashboard and A/C system.

Michael Neal recommends shortcutting the heater core removal to keep from pulling the dash apart. The instrument pod must still be removed, and dropping the steering column down is required. But total disassembly can be avoided by cutting the pipes and installing the new core using short pieces of hose with clamps. Neal is an official Jaguar mechanic and highly recommends this method; there is nothing wrong with using heater hose for such an application, and disassembly of the entire system is likely to cause further problems unless done by an experienced Jag mechanic.

Greg Price sends a detailed checklist: "To those who have to replace their heater cores and want to cut the pipes rather than disembowel their entire interior, the procedure is pretty straightforward with the following caveats:

1. You don't have to take the driver's seat out, but it might make a more comfortable working environment.

2. The steering column must be removed in order to make room for the heater core to slide out. The steering column is held up under the dash by four bolts. These bolts have spacers, washers, seating rings and a steel piece that holds the nuts. Before removing the steering column, take out the tach and speedo, then look inside with a flashlight to see where all of the little spacers and miscellaneous bits go. Take notes. As soon as you start to remove the four bolts, all of those bits bail out.

3. Take a Polaroid picture of the heater mechanism area before you start taking things out. If you can't buy or steal a Polaroid camera, draw a very detailed map of the area, and pay attention to what goes under or over what.

4. As you remove the screws and such, tape them to a sheet of paper in the order that they were removed. It makes the orderly reassembly that much more orderly.

5. Buy the best hose clamps you can find. Get those swedish jobs that you can torque down with an impact wrench.

6. Use silicone to seal the hose to the pipes.

7. Cover everything. Twice. Brass shavings fly everywhere when you cut the pipes (especially if you use a pneumatic cutoff tool). Silicone always ends up everywhere except where you want it.

8. Be mindful of the hazard light switch. It's easily mangled. I think mine will hold together (I hope).

9. Plastic wire ties are great for holding all of the excess wiring and plumbing up out of your way.

10. Don't drain your cooling system like the manual says. Pull off the heater hoses, plug them temporarily, then blow the remaining water out of your heater core with compressed air. Keep your face away from the outlet.

11. Watch out for the fiber optic line going into the ignition switch cover. Remove the switch cover and tape it up out of the way with the fiber line before you drop the steering column.

12. If your cruise control doesn't work, now is a good time to check the steering column wiring and speed set switch.

"The entire procedure took me about 3 and a half hours (including a short dinner break), which beats the hell out of disassembling the dash and console."


BLOWER FANS -- REMOVAL: Fortunately, the blower fans are a lot easier to remove than the heater core. 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.


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?

Remove the C-clip from the shaft, and remove the stack of washers against the front bearing; be sure to keep track of the washers and the order they are installed in. Turn the shaft and observe the front bearing, which should remain motionless within the housing. If the bearing turns with the shaft, a positive anti-rotation modification is called for. One method is to drill a hole through the steel housing and into the bronze bearing and install a tiny self-tapping screw. Make sure the tip of the screw doesn't contact the shaft itself, and that the head doesn't interfere with the C-clip and washers.

Pull the little covers off the brushes and remove them. If they are too short, replace them; don't bother trying to find original Jaguar brushes, just find some slightly larger at a motor or vacuum cleaner shop and file them down to size.

While the brushes are out, use a VOM to check the continuity at the segments of the commutator. There should be some form of continuity between any two segments you test. If you find a segment that doesn't seem to connect to anything, you're in trouble. If you can see why (a winding disconnected or some such) you can decide for yourself if it's possible to fix. Don't use any solder, it won't take the heat, connections must be made mechanically or by tack welding.

If you're like me, you'll grind a small flat on the shaft for the setscrew in the impeller. I just don't like setscrews on a plain shaft.

Before reassembly, inspect the condition of the three rubber mounts. If they are dry and hard or crumbling, renew or fashion suitable replacements from grommets, hose, whatever.

If your blower fans are toast, Vicarage carries replacements at reasonable prices.


BLOWER FANS - REINSTALLATION: The rubber duct may be a neat feature, but it can be a real pain to reinstall. To make life easier, attach the duct securely to the blower assembly before installation. I suggest the use of aluminum tape.


BLOWER FANS - INDIVIDUAL SPEEDS NOT WORKING: The four blower speeds are controlled by four relays built into a single unit that is located adjacent to the left side footwell; the footwell register and the small padded cover must be removed to get at it. If one of these four relays quits, one speed of the blowers no longer works, and the A/C system just skips over it from the next lower speed to the next higher speed and back. The result can be a little disconcerting, since the bigger change is speed is quite noticeable, and since it may be more change than necessary the system can end up cycling back and forth between the two speeds a lot when it would have been happier just staying at the middle speed. Even worse, if it happens to be the "low" speed relay that fails, the A/C compressor can be operated without a fan running which is not good on the equipment and may cause the compressor to kick in and out on its own thermostat trying to prevent iceup.

This four-relay assembly appears to be a common failure: this author has had three of the four relays inside it fail, and others report similar results.

I took the box apart and fixed it each time. The unit is tough to get out of the car, but once out it is a simple matter to bend the plastic edges back and pry open; you might even try bending the edges back and prying the base out without removing it from the car, since the base will carry all the important parts and you'll simply leave the plastic housing in place. Be careful; the NW wires connecting to the terminal with the screw (and several of the components inside, if you don't disconnect this wire before opening) are hot at all times unless you have disconnected the battery.

The coils are designed to be on continuously, so they don't burn up; the problem always seems to be broken connections. The thin wires from the relay coils break off of the terminals, and soldering them back on makes it work as good as new. However, there is a theory that these long thin wires spanning considerable distances within this assembly are the cause of the problems; a vibration in the car, perhaps at a particular speed or engine RPM, may resonate these wires like guitar strings and break them off.

So, instead of just reconnecting them, fix the problem. On each coil, the skinny coil wire comes out of the coil and is wrapped a couple of times around a plastic lug on the side of the coil before running off to the terminal. Solder a larger gauge wire to the terminal and route this larger wire to the plastic lug on the relay and wrap it around a couple times, then solder the end of the coil wire and the new thicker wire together right next to the lug. Hence, the thick wire spans the distance to the lug, and the thin coil wire is well supported.

Alternatively, just replace the individual relays that go bad. Brian Sherwood "Found a portion of the fan control relay was inop, no fan on "low". Removed four wires from bad portion of relay block and plugged into a generic 12-volt relay with spade terminals; fan works fine now. Fan control relay is located in center console, LH side under heater unit."

The four relays are located at the four corners of the unit. The "low" relay, at the bottom right corner as you look at it, seems to be wired with four wires as Sherwood described. The other three relays, however, each have two wires going to them, plus there are two commons going to the whole set of three. A large NW wire provides 12V power to all three contacts to power the blowers. A small BU wire provides a common switched ground for all three coils. The signal to the relays comes via BY, BG and BW wires, and the power to the resistor pack and blowers is via larger U, R, and GS wires.

If the low relay fails, you can replace it with a standard automotive relay, such as those sold for driving lights; merely remove the four wires from the box and connect the B and NY wires to the coil and the NW and Y wires to the contacts, as Sherwood suggests.

If one of the other three relays fails, you can still replace it with a standard relay. Connect a wire from the BU wire to one side of the coil (without disconnecting the BU wire from the other relays on the board), and simply pull the BY, BG or BW wire off the terminal on the faulty component and connect it to the other side of the coil. Connect a heavy wire from the NW wire to one side of the contacts (again leaving it connected to the other circuits), and pull the U, R or GS wire from the terminal on the faulty component and connect it to the other side of the contacts.

Either opening the box and correcting the problems or replacing the relays with individual SP relays would probably save a lot of money; generic "driving light relays" will work fine are only a couple bucks each. It's likely to cause less trouble, too; most of the aftermarket generic relays are quite reliable. You certainly don't want to buy a replacement four-relay unit from Jaguar -- after all, the original one is causing trouble, and the replacement isn't likely to be any better. In fact, it might not be a bad idea to simply yank the entire block out of the car and replace it altogether with four generic relays at the first sign of trouble.

Note that British Leyland Service Division Training Manual S1002 on the Environmental Control System shows a separate low speed relay and a box containing three relays; since the manual is intended for the XJ6 and XJ12 Series Two, this probably describes an early arrangement. The wiring schematic appears unchanged, however, and the replacement of individual speed relays with separate units will work just as well.



BLOWER FAN RESISTOR PACK: Component #188 on the schematics. Physically, this unit is mounted in an opening high on the left side of the A/C system, above the heater core pipes. Access to the resistor pack is poor, to put it mildly. If it must be removed, it is suggested that the left side blower assembly be removed first. It is also suggested that a small hole be drilled in a piece of structural sheet metal to allow a Phillips screwdriver to be used on the upper mounting screw.

For those who need to analyze or repair the resistor unit, the details are shown in Figure 12. Note that the resistances shown are as measured on the unit in the author's car, which appeared to be in excellent condition. The values seem to represent consistently higher ohmage than in the Jaguar official wiring diagrams, but the overall scheme is the same.

The speed of the blower fans is controlled simply by connecting the various resistances in series with the blower motors. These resistor packs are installed in the airstream from the blowers so that the airflow will keep the resistors cool. If the blowers seize or otherwise fail to move air, the result is often a cooked resistor unit due to lack of cooling combined with the high current load due to the mechanical problem.

If one is really cheap or in a hurry, the unit can always be repaired using Nichrome wire from an old toaster or some such, or even by twisting severed wires back together. Do not use solder, as it will melt; all connections must be mechanically attached. Exact resistance values are unimportant, since being off a little will only make the fans run a little faster or slower than original. Note that this unit is so difficult to get to that it would be nice to make real sure it doesn't fail again.


BLOWER FAN RESISTOR PACK -- FUN WITH SCHEMATICS: The A/C system schematics in the owner's manual (my copy, anyway) and the Haynes repair manual #478 (page 240) show the blower fan resistor pack (component 188) incorrectly. They show the GS wire to the fan motors themselves being connected to one end of the three resistances, as though all three resistances operate in series. In fact, the GS wire connects between the 0.85 and 0.425 resistances (as shown in the illustration above, except the as-measured resistances are 1.2 and 0.6 respectively). In M1 speed, power is supplied to both ends of the resistor pack (Y and U wires) so that the 0.85 resistor operates in parallel with the 0.425-1.275 pair. In M2 speed, power is supplied to the R wire in addition, so the 0.85 resistor is now operating in parallel with the 0.425 alone.

The system schematic in the Jaguar repair manual at the end of section 86 shows the fan resistor pack correctly.

Also of note, the schematic in the Jag manual shows one additional circuit by which the high speed position of the control knob will, via diode #D4, operate the M2 relay. Reason unknown; it almost appears as a backup in case the high speed relay fails.


DEMIST DUCT VANE: The official Jaguar XJ-S Repair Operation Manual, Section 82.25.21, step 35 says "Ease demist duct vane securing studs from screen rail and recover demist duct assembly." John Nuttall felt this was unclear, so when he finally figured out what it was talking about he provided the following explanation. Note this applies to his 1977 XJ-S.

"Removal of this vane uncovers a screw which secures the unit to the car body just below the windshield. The main difficulty with the manual is that it does not make clear just what is the demist duct vane, and I don't think the official name is a very good description. It turns out that this object is a piece of vinyl covered rubber about 34 in (85 cm) long, 3/4 in (2 cm ) thick, and 3in (8 cm) wide in the centre, tapering at the ends. Along its back face is screwed (with 13 screws) a plastic air deflector to direct air to the windshield. This vane fills in the gap between the centre of the fascia and the windshield.

"To remove the demist duct vane you must undo two screws placed vertically downwards at the ends. With the windshield in place it is impossible to do this with a conventional screwdriver. I was able to turn these screws with vise grips. The underside of the vane has two prongs about 17 in (44 cm) apart which engage slots in the unit below."


CONTROLS: Rob Reilly provides the following system description: "Outside air is drawn in through the grille in the center of the cowl between the bonnet and the windshield. Vacuum operated flaps on the fan motors close off this outside air under certain conditions and draw air instead from inside the car (known as the recirculating mode).

"From the fan motors the air goes through rubber branch hoses to the front chamber of the heater unit. Here all the air passes through the air conditioning evaporator and gets cold (if the compressor is on). Then there are four flaps controlled by mechanical linkages which can be seen on the right hand side of the unit. These control what percentage of the air passes through the heater core and becomes warm (if the water valve is open and the water is warm) on its way out to the vents.

"The upper front (meaning toward front of car) flap ("upper bypass flap") opens or shuts off cold air to the dashboard side vents, center vent, and windshield defrost vents. This air has not passed through the heater core. Clockwise is open, counterclockwise is closed, viewed from the right hand side. The center vent and windshield defrost vents also have vacuum-operated flaps.

"The upper rear flap ("upper heater flap") opens or shuts off warm air, which has passed through the heater core, to the same upper vents as the first flap. Clockwise is closed.

"The lower rear flap ("lower heater flap") controls warm air to the lower vents on the sides of the transmission hump and to the duct hoses going to the rear vents under the center console armrest. Clockwise is open.

"The lower front flap ("lower bypass flap") controls cold air to the lower vents. Clockwise is closed.

"On the left side is a vacuum actuator and linkage which, when the selector is on DEFROST, will be up (vacuum off) and prevents the bottom heater flap from opening.

"There is a servo motor on the lower right which operates some more micro-switches, vacuum line valves, and mechanical linkages, and is in turn controlled by the temperature setting and several temperature sensors through the amplifier and relay on the lower left.

"The left hand knob (temperature control) turns a variable resistor. The resistor should have a resistance of zero ohms at the 85 degree mark and 10,000 ohms at the 65 degree setting. There are three solder pins on this thing, one of which should not be used. If you had a high resistance in the circuit the unit would think you're asking for cold air and would turn the stepping motor to give it to you.

"The small device mounted on the lower tube of the heater core is a temperature-controlled on/off switch which disables the blowers until the water warms up." Actually, it limits the blowers to low speed.


CONTROLS -- VACUUM LOGIC: The following logic chart was graciously provided by John G. Napoli:


Jaguar Climate Control Vacuum Logic -- Representative of 1982 XJ-S HE
Compiled by John G. Napoli







Vacuum Solenoid


Item Con-trolled:

Screen Flap

Lower Heater Flap

Water Valve

Center Dash Flap

Blower Flaps


Control Status:






Item Status:


Open, and over-ridden by flap




Vacuum Status:







Control Status:






Item Status:






Vacuum Status:



No Vacuum

No Vacuum

No Vacuum


Control Status:






Item Status:






Vacuum Status:

No Vacuum

No Vacuum

No Vacuum

No Vacuum

No Vacuum


  1. In FULL COOL, recirculation is enabled because the vacuum solenoid is energized.
  2. A NORMAL A/C mode is therefore implied with the vacuum solenoid de-energized.
  3. In FULL COOL, everything gets vacuum.
  4. In FULL DEFROST, nothing gets vacuum (default system operation if system fails).
  5. In FULL HEAT, only the items fed by the vacuum switch get vacuum.
  6. The vacuum switch is attached to the right hand climate control knob (Positions: Low, Auto, High, Defrost).
  7. The cam switches are part of the servo. The servo is mounted on the right of the climate control unit under the dash (next to the right hand occupant's left shinbone).
  8. The vacuum solenoid is mounted on the left of the climate control unit under the dash (next to the left hand occupant's right shinbone).
  9. Water valve is located on center of firewall in engine compartment.
  10. Dashboard may have to be removed to access flaps. Always check operation of and adjustment of servo linkages when troubleshooting this system. There are two blowers (left and right). Check them both!
  11. Some later XJ-S's may have a manual override enabled by pulling the right hand climate control knob out and turning. Reference to this feature was seen in a 1983 XJ-S Owner's Manual.



CONTROL MICROSWITCHES: The right side control knob has microswitches behind it that are often found to be the source of trouble. However, Ron Whiston points out that the problem is often not a failure of the microswitches themselves, but simply that they are incorrectly positioned relative to the cam; turning the knob doesn't move the switch enough to make it click. Even though the mount holes are not slotted and are not intended to provide any position adjustment, merely loosening all the mount screws and holding the switches inward while tightening them back down will often correct all problems.


TEMPERATURE CONTROLLER: Reportedly, the wirewound pot has problems.


CONTROL LINKAGE ADJUSTMENT: The Jaguar repair manual describes an adjustment procedure that is unclear and covers only a couple of the adjustments needed. The illustrations are tiny and poorly labeled. Below is a procedure that should enable a more complete adjustment of the linkage. See Figure 13 and Figure 14.

While performing these adjustments, keep this concept in mind: The difference between a flap being fully open and 90% open is insignificant; there is a lot of airflow in either case, and the passenger will not be able to detect a difference. On the other hand, the difference between a flap that is fully closed and one that is slightly open is huge. Therefore, the objective of the adjustment procedure is to make sure that all flaps close fully, and how far they open will be of little concern.

1. Remove the glove compartment, the "underscuttle casing" (panel above the footwell) on the right side, and the grille and padded panel on the right side of the transmission tunnel.

2. Remove the short steel duct that serves the footwell grille. Be careful not to drop any screws into the works.

3. Loosen the locking screw on the lower bypass flap adjustable link. Loosen the locking screw on the upper heater flap adjustable link if there is one; if the car has a facia temperature control (a slider under the stereo), it will not have an upper heater flap adjustable link as the facia control takes its place. Loosen the locking screws on both pullrods where they connect to the servo control levers.

4. Move the servo to the full cool position, which is where the levers on the servo are held at their most downward position. Note that the pullrods are normally held upward by the linkage springs; with the linkages disconnected, the servo levers will fall down regardless of servo motor operation. You must pull upward on them with your fingers to determine what position the servo is actually in. Note also that operation of the servo doesn't move the levers continuously from one extreme to the other, but rather goes back and forth somewhat; be sure the motor has moved all the way to the extreme position that holds the levers in the downward position before proceeding.

To move the servo, disconnect the main electrical connector to the servo unit, which is a 13-wire connector in the same general area you're already working in. Connect 12V power across the solid purple and solid red wires; if the battery is connected, 12V power is available at the nearby fusebox, at fuses 2 or 3 (RHD cars) or fuses 13, 14, 15, or 16 (LHD cars) so it's a simple matter to run a jumper from the fusebox -- or simply from the cigar lighter, and connect the other wire to ground. If the battery is disconnected, a 9V battery will also work well, running the servo a little slow but it gets there. To run the opposite direction, reverse the power.

5. Turn the main bellcrank clockwise until the lower heater flap is held firmly shut; it may be easier if the main tension spring is disconnected. Hold the main servo control lever up. Tighten the locking screw on the servo lever.

6. If the car has no facia control, hold the upper heater flap in the fully closed position (clockwise) and tighten the locking screw on the adjustable link.

If the car has the facia control, move the slider to the full right position. Loosen the clamp holding the cable housing, and move the cable housing until the upper heater flap link forms a straight line. Lock the cable housing into this position.

To check the operation of the facia control, move the slider to the left. The upper heater flap should fully close, and further movement should be taken up by the spring in the linkage.

7. Move the servo to the full heat position (levers in their highest position).

8. Turn the lower bypass flap to the fully closed position (clockwise). While holding this position, slide the adjustable link to its longest possible length and tighten the locking screw.

The lower bypass adjustable link has a slotted opening to allow the flap to be farther closed than the linkage calls for. To check that this slider works properly, move the servo off the full heat position. Turn the lower bypass flap towards closed, against the force of its spring. The lever should move smoothly in the slotted hole. If it doesn't move smoothly the linkage is probably misaligned, causing it to jam. Determine which way the parts are misaligned. Take the lower bypass adjustable link apart by removing the locking screw entirely and removing the screw holding the lever to the flap. Once out of the car, carefully bend the parts to correct the misalignment. Reinstall, readjust, and check for proper motion again.

9. With the servo in full heat position, allow the spring to turn the upper bellcrank clockwise until the upper bypass flap is closed. Hold the upper servo lever up and tighten the locking screw.

10. Reassemble and test drive.

Note that on later cars there is a vacuum actuator on the left side that holds the lower heater flap closed when the defrost is called for. Vacuum permits lower heater flap operation, lack of vacuum prevents it. To observe the operation of this actuator, it will be necessary to remove the underscuttle casing on the left side. There is no real adjustment necessary, however, since it is either on or off. Make sure there are no wires or anything obstructing its motion.

Note that the connection of the pullrods to the bellcranks is a nut-bushing that is fitted into a slotted hole on the bellcrank. The procedure above does not address location of the nut-bushing within the slotted hole. This position determines the sensitivity of the system; if the motion of the servo causes the flaps to move too much, the nut-bushing should be relocated farther away from the pivot so that the same amount of pullrod motion won't turn the bellcrank so much, and vice versa if the servo doesn't move the flaps enough. It is recommended that these nut-bushings not be tampered with. If their position is altered, the entire linkage adjustment procedure above should be repeated.


CONTROLS - RANGE PROBLEMS: Olov Carlsson sends this comment: "I had a problem with the temperature control knob being out of range. Even when I put it in the coldest position, the system wouldn't cool properly. It did work, however, which I determined by using the cigarette lighter and holding it under the interior temperature sensor. This sits in a hole that can be felt under the dashboard centre shelf. When doing this the system adjusted itself and cranked out wonderfully cool air.

"There is an adjustment for this on the amplifier unit. I turned it to the cold end position, but this wasn't sufficient to bring the temperature control knob properly on scale.

"My final solution to this was to connect a 10 kohm resistor in parallel with the external temperature sensor, which is mounted inside the right side external air intake. Careful analysis of the circuit diagram and the wiring allowed me to put the resistor alongside the internal temperature sensor. I connected a wire to the appropriate lead on the amplifier unit, the result being that the new resistor effectively was in parallel with the external temperature sensor. This one, by the way, did measure the correct resistance (the same as the internal sensor, when they both had the same temperature). This brought the adjustment on the amplifier unit into range making it possible to calibrate the temperature control knob."


TOO MUCH COOLING: Mike Morrin says, "If the system works properly for a while (10 minutes) and then drifts slowly towards full cooling, then the fault is likely to be in the plumbing to the in-car air temperature sensor. This is a reference to a couple of cases I have heard of where the rubber connector inside the dash had come adrift so that the air temperature inside the dash was being measured. There is no cold air supply inside the dash, just heat soak from the engine and heater unit, causing the measured temperature to creep higher and higher, and the A/C to pump full cold into the car."


TOO MUCH HEATING: Tom Bernett says, "Note that the function switch removes the supply from the temperature control circuit when in the DEF position, and this causes the system to move to full heating, so a faulty function switch can cause the system to stay on full heating. But, I was getting considerable air flow from the side and center vents when it was in full heat mode."

Mike Morrin explains: "Yes, because the function switch also has a vacuum valve which directly controls the demist flaps, and is independent of the electric circuit."


SERVO REPAIR: Mike Morrin says, "After cruising for an hour at about 70 mph. with the A/C on (of course), the system all of a sudden went to full heat. I fooled around with the temp selector and after several minutes it went back to normal operation.

"It turned out to be a faulty feedback potentiometer in the servo, so that the amplifier thought the system was on full cold, so was sending the system to full warm. To check this you need to leave a voltmeter connected to the feedback circuit (as per instructions) and see if the voltage goes the right way or the wrong way when the fault occurs.

"The actual fault on mine was that the feedback potentiometer is a wirewound type, and the wiper arm had worn through the wire right at the end of its travel. I did a quick fix by painting some silver loaded paint onto the end of the winding, and it has survived for 3 months so far, I expect another 10 years out of it."


RELAY CHATTER: Mike Morrin, who owns a 1975 XJ-S, reports on "a tendency for the amplifier relays to chatter after moving the servo. An oscilloscope across the supply lines showed noticable spikes when the amplifier relays operated. I have managed to significantly improve this by fitting a 1000 uF 50V capacitor across the 12V supply close to the amplifier. The amount of relay chatter is reduced by about 80%. I can confirm that driving the car today, the operation of the servo system was smoother than previously."


CONTROL AMPLIFIER REPLACEMENT: Aftermarket A/C control system amplifiers are available for those who either don't wanna pay Jaguar prices or don't expect that a new one of the same type will last any longer than the original did. See H. D. Rogers & Sons.


CONTROL AMPLIFIER REPLACEMENT -- CHEAP VERSION: Mike Morrin suggests, "...a double pole switch (like a window lifter switch) can be arranged to drive the servo manually." Simply connect 12V power through the switch to the red and purple wires on the servo connector; the two positions of the switch should provide power in opposite polarities. Label the button "cooler" and "warmer" or some such.



1987-On System (Delanair MkIII)


PARTS: Parts for the MkIII system are notoriously expensive. Per Hal Rogers, "the Delanair heater unit is made/supplied by Delanair of England. Many aftermarket companies have attempted to obtain parts directly from Delanair but they cannot sell directly because of contractual obligations to Jaguar."


PARTS CONFUSION: According to Technical Service Bulletin #8228, there is some confusion as to which A/C ECU goes with which water temp switch and in which car. According to their guide, the trick is to check the wires at the water temp switch on the left side of the evaporator case. If the wires to this switch are slate and black, the correct ECU is CAC 8032, the correct water temperature switch is JLM 763 (red), and the harness part number is JLM 1170. If the wires are green and black, the correct ECU is DAC 7601, the correct water temperature switch is JLM 2121 (black), and the harness is either JLM 10393 (all convertibles and 1992-on coupes) or JLM 10394 (1991-92 coupes). We all clear on that? Good.


VACUUM SCHEMATIC: Finding a vacuum schematic seems to be difficult, so I have included two here -- courtesy of Victor Naumann. Schematic 1, Schematic 2.


BLOWER FANS: According to Randy Wilson: "Jaguar doesn't sell the blower separately. They sell the complete blower unit: housing, motor, fan, and electronics! Yes, there are electronics buried inside that blower case. Plus, just to add a bit more, the right hand box carries the ambient temp sensor. There are also two relays inside the box." The blower assembly is reportedly incredibly expensive.


BLOWER SPEED CONTROL REPAIR: Stefan Knappe saved himself a lot of money: "I noticed that the right fan (it's got two, left and right) did not work except when the fan speed was set to max. I took the blower motor out, which is rather easy on the right side of a LHD car, finding a little solid state circuit located in the intake part of the fan. This circuit gets information from the A/C computer and regulates the fan speed unless the setting is to max, which actuates a little relay situated in the blower case too. I found out that the power transistor on this little circuit was blown. I went to the Jag service asking whether this is available seperately. But, you might have guessed it, the blower is only available as a complete assembly, being very expensive. So I went to an electronic store and bought a transistor equivalent to the type built into the fan-circuit (Texas Instruments #2N6284). I soldered it in, put the stuff together and the fan worked from that time on without problem."

Martin Sellars adds, "Air con blowers: these devices contain an electronic circuit which gives speed control for all settings but "high". This comprises a Darlington transistor 2N6284, a 68 Ohm 2.5Watt resistor, a 1N5401 diode and a small glass diode, probably 1N4148 or 1N914. All these parts are easily obtained cheaply from electronic component outlets (example; in the UK Farnell Electronic Components, +113 2636311, but ask for a catalogue to get the right order numbers). Blowers that won't run at low speeds almost always have a failed transistor, but replacing that alone won't always fix the fault. The resistor is there to protect the transistor from voltage spikes produced by the motor, so check the value and replace if it isn't right (most hobby multimeters have an Ohms measurement feature). The small diode feeds the blower motor voltage back to the AC computer, and has steel leads which corrode away, breaking the connection and preventing speed control from working. I replaced mine with 1N4004 types, which are much more rugged, more easily handled, and cost just a few pennies more. These diodes are fitted with their cathodes (marked by a bar on the body) towards the transistor collector (the steel case). The 1N5401 diodes are very rugged, and unlikely to need replacing. When fitting new diodes or resistors, don't try to fit them inside the blower interior, like the originals, where they are prone to corrosion. Fit them on the solder side of the PCB (having snipped out the old parts) and then cover them with the original plastic flap using some tape.

"I also fitted new brushes to the blower motors, using power drill spares filed down to the right size (Kirby's tip!).

"Inside the blower assembly is the high speed relay, which is also prone to dirt and corrosion. Standard car accessory shop units can be used here, but check the pinout - I think they are not standard, I had to rewire mine. Considering the cost of a new unit, changing the parts mentioned above gives "as new" performance at a tiny fraction of the cost."


COMPUTER PROBLEMS WITH BLOWER CONTROL: Stefan Knappe cheated on this one: "Another problem I had on a friend's car, on which one fan did not work. After checking the fan, I found that the A/C computer (located on the right hand side of the centre console, take cover underneath glove box out) delivered signal to one fan blower only, the other signal line being dead. Computer gone (at least in this respect). I asked for the price of a new one and decided immediately to go for another solution. Since I'm not so deep into electronics to repair this difficult thing itself, I had another idea. I cut the signal line which was dead and connected it (the line to the blower) with the good one for the other side. Both fans worked again. Risk was that the computer will be damaged on the good side due to higher current delivering two circuitries, but on the other hand the thing was already gone... This solution proved to be okay, since it still works and the repair has been done three years ago.

"Caution: Don't check power output anywhere in the system with a lamp or bulb, use a voltmeter 10 MOhm impedance, otherwise you may damage the computer!!"


TEMPERATURE SENSORS: Martin Sellars says, "Temperature Sensors: the Delanaire system uses three, all are electrically identical. They measure ambient air temperature (mounted on the RH blower housing), in car temperature (above the glove box, behind a small aperture in the dash) and on the evaporator. These have three wires to them, power (5Volts from the ACC), ground, and the output wire. The output voltage is very closely controlled at 2.785V at 0イ and rising by 0.01V per degree C. So, a sensor at 20イ (about 68ェ) should read 2.985V, and at 30イ (about 90ェ) should read 3.085V, and so on. I found these can be measured reasonably easily with a standard 20k/Volt moving needle "hobby" type multimeter, at least well enought for fault finding purposes."

Richard Mansell quotes from a Jaguar publication on the changes for the 1992 model year:

The air-conditioning in car sensor now uses the motorised aspirator/sensor from the XJ6 allowing a more accurate reading of the true temperature of the cabin which will be less susceptible to drift or overshoot.



DUMB PROBLEMS: Martin Sellars: "My car showed very erratic operation of the A/C, sometimes OK, sometimes wrong settings (hot on hot days and vice versa!), sometimes no action at all. This fault might have been blamed on the computer - but in fact it was due to moisture coming out of the evaporator, and running down the RHS of the transmission tunnel onto the single in-line fuse holder that carries the supply current to the A/C computer. The contacts had corroded slightly, breaking the supply current, and giving intermittent operation of the A/C. A new inline fuse, plus fixing the drainage, solved the problem."


WHILE YOU HAVE THE BLOWERS OUT: Martin Sellars: "While the blowers are out, access to the evaporator is much easier. The four short tubes which couple the evaporator body to the rubber blower ducts can be twisted slightly and removed. This allows slight access to extract some of the gunge and detritus that blocks up the drainage system, causing wet carpets, rusty floors, and other problems."


HEATER CORE REPLACEMENT: Those who must replace the heater core should thank their lucky stars if they have the Delanair MkIII system. A major design feature of this system is the ease of replacing this core, a major task on the earlier cars. The Delanair MkIII system has bolt-on pipes for the heater core, eliminating the need for the "shortcut" pipe-cutting procedure devised for the earlier system. Also, Per Michael Neal, "The heater core is removable from the right side. There is a large piece of black tape, similar to electrical tape, that covers the access panel. Removal of the core is simple as unbolting the pipes, pulling the glovebox and access cover and removing the core." This eliminates the need for removing the instrument panel and dropping the steering column, as on earlier models.


HEATER CORE PIPE ATTACHMENT BOLTS: Per Julian Mullaney, "There was a problem of dissimilar metals causing corrosion of the bolts which attach the pipes to the brass core. The pipes and heater core are brass, the screws holding them together were steel. I guess stainless bolts would be better. You could replace them as a preventive measure."


HEATER CORE PIPE ATTACHMENT O-RING SEALS: Per Julian Mullaney, "The O-ring seal used at the connection point appears to be of a terrible design. A mechanic once told me that these O-rings always go first."

For anyone who doesn't think the resultant leaks would be a big deal, Mullaney adds: "This leak really screwed up a lot of stuff under there. The drips ruined the A/C amp, connectors, and my CD player."

Apparently Jaguar realized the seriousness of this problem. According to Michael Neal, "Jaguar has a gasket to replace the O-rings. It is shaped like the mating pipe of the heater core and is made out of a silicon/rubber type material." The part number for the gasket is JLM 759; you need two to do the job.

According to Mark Roberts, the "condensation deflector shield" being added to systems by Jaguar is actually a result of these connections leaking on radios!



On to the Electrical System


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