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XJ-S Air Conditioner & Heater

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XJ-S 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.

Common Features

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.

Air Conditioner Compressor

The Jaguar A/C compressor is 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.

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 compressor also may not fit the protection switch that was in the original compressor. Read the section below.

Compressor Protection Circuit

Just below the inlet and outlet connections on the 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.

Compressor Front Bracket

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.

Compressor Removal and Refitting

The mounting of the A/C compressor is a little hokey, in that the rear end is very firmly located and any tolerance in dimensions must be taken up by flexing the 1/4" thick plate (!) supporting the front. There are no slotted holes or the like. Fortunately, the system seems to work provided you assemble and disassemble in the correct 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.


Apparently, the receiver drier unit on some Jags has O-ring fittings; on other Jags, the unit has flared fittings on it. Either one should be readily available.

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 tarlike 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.

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 6695730 or Monroe Air Tech at 1-800 4243836.


Other possibilities include a host of up-and-coming substitute refrigerants such as Hot-Shot or GHGX4 (GHG in honor of the chemist who put the formula together, George H. Goble), all supposedly direct replacements for R-12 with little or no conversion necessary. Note, however, that these refrigerants are NOT YET approved for use in automobiles.

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.


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 as described on page 11.

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 frontmost '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 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.

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.

On the 1983 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.

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 valve causes problems, you can take it to an auto parts shop or auto A/C shop and ask for a Chevy valve that has the same size hose connections. The Chevy valves are a butterfly type and are made of plastic and stainless steel, and weigh so little that they don't need to be mounted; they can merely be suspended in the hose. They also cost only about US$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.

An even better option is to replace it with a Jaguar valve! The newer XJ's use a valve made entirely of plastic -- no metal at all -- and cost half what the Chevy valves cost. Although some people don't like plastic, the design of this valve is so superior that it is probably the most reliable choice; since it is a poppet valve rather than a rotating-cylinder valve like the Jaguar original or a butterfly like the Chevy valve, the reliability of a total shutoff when closed is much better than either. Reportedly, Pep Boys sells an aftermarket version of this valve made by Factory Air, part no. 74803.

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.

Pre-1987 A/C System

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.

Blower Fans

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.

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.


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.

Individual Speeds Not Working

Brian Sherwood had this experience:

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.

This is good advice, and would probably save a lot of money; generic relays are only a couple bucks each. I will endeavor to make the description clearer. The four blower speeds are controlled by four relays built into a single box that is located adjacent to the left side footwell; the footwell register and the small padded cover must be removed to get at it.

The four relays are located at the four corners of the unit. The "low" relay seems to be wired as described, with four wires. The other three relays, however, each have two wires going to them, plus there are two commons going to the whole set. A large NW wire provides 12V power to all three contacts to power the blowers. A small BU wire provides a common 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.

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 faulty connector 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 faulty connector and connect it to the other side of the contacts.

Blower Fan Resistor Pack

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 5. 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 do not appear to agree with the Jaguar official wiring diagrams.

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.

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.


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 microswitches, 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.

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 Switch

Cam Switch

Vacuum Solenoid

Item Controlled

Screen Flap

Lower Heater Flap

Water Valve

Center Dash Flap

Blower Flaps

Full Cool

Control Status






Item Status


Open, and over-ridden by flap




Vacuum Status



No Vacuum

No Vacuum

No Vacuum

Full Heat

Control Status






Item Status






Vacuum Status



No Vacuum

No Vacuum

No Vacuum

Full Defrost

Control Status






Item Status






Vacuum Status

No Vacuum

No Vacuum

No Vacuum

No Vacuum

No Vacuum


  • In FULL COOL, recirculation is enabled because the vacuum solenoid is energized.
  • A NORMAL A/C mode is therefore implied with the vacuum solenoid de-energized.
  • In FULL COOL, everything gets vacuum.
  • In FULL DEFROST, nothing gets vacuum (default system operation if system fails).
  • In FULL HEAT, only the items fed by the vacuum switch get vacuum.
  • The vacuum switch is attached to the right hand climate control knob (Positions: Low, Auto, High, Defrost).
  • 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).
  • 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).
  • Water valve is located on center of firewall in engine compartment.
  • 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!
  • 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.

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 6 and Figure 7.

Figure 6 - Heater Control Linkage -- Early Models

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 very significant. 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.

Figure 7 - Heater Control Linkage -- Later Models

  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 cold 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 springs; with the linkages disconnected, the servo levers will fall to their lowest position 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. Connect 12V power across the solid purple and solid red wires; a 9V battery works 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 hot position (levers in their highest position).
  8. Turn the bottom 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 bottom 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 bottom 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 bottom 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 bottom heater flap closed when the defrost is called for. Vacuum permits bottom 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.

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.

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.

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.

Blower Fans

According to Randy K. 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.

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.

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.

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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