Jaguar XJ-S. Manual - part 136

 
 

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down, all bets are off; open windows are detrimental to aerodynamics, and if you’re travelling at highway speeds 
the benefits of turning the compressor off and opening the windows may be a wash. 

One final note:  The stock system will already shut off the compressor under either of two conditions: 1) the air 
coming through the evaporator coil is too cold, or 2) the system is calling for max heat.  Hence, the Napoli mod 
should not actually increase the heating capacity of the system; when max heat is needed, the compressor is off 
anyway.  If this mod does noticeably improve heating performance, there is something wrong in the control system; 
I’d recommend adjusting the flaps per the procedure on page 533. 

 

GARDNER MOD:  The system is clearly designed with the intention that you will always have the climate control 
system on when driving; when the system control knob is turned to the “OFF” position, the fresh air/recirculation 
flaps are moved to recirc position, positively closing off the intake of fresh air.  Tony Gardner’s mod lets you drive 
along with the climate control system switched off and still have nice fresh air wafting through the dash vents.  The 
Gardner switch removes the ground from the vacuum solenoid controlling the fresh air flaps, allowing the flaps to 
open and fresh air to enter the cabin. 

The vacuum solenoid in question is readily accessable; simply remove the grille and pad on the left side of the 
console, and the vacuum solenoid is mounted just forward of the four-relay box.  Simply disconnect the ground 
wire, and connect it through a switch. 

The Gardner switch will hold the fresh air vents open regardless of whether the system is on or off, but when the 
system is on there isn’t much point.  During normal operation, the system almost always keeps the fresh air intakes 
open; the only time they are closed are during max cool and max heat, which are relatively rare.  However, as noted 
above, the Napoli mod may cause the control to run to max cool far more often, so the Gardner mod may come in 
handy to use in concert with it. 

For winter use, Gardner himself provides the following tip:  “If the climate control is set to heat (to adjust the flaps) 
and then switched off, warm air flows through the fresh air ducts.  The vent mod does not replace AC, therefore it 
actually works better in winter than summer.”  Note that when the system is switched off, the heater valve remains 
open for coolant to freely flow through the heater core; Gardner’s idea of setting the temperature to full heat and 
then shutting the system off merely leaves the flaps in a position to guide the wafting air through the heater core.  If 
the temperature is set to full cool and the system is shut off, the flaps will remain in a position to bypass the airflow 
around the heater core. 

 

GARDNER/NAPOLI MOD COMBINATION:  Tom Bernett was concerned about locating a profusion of switches 
in his XJ6.  “If you combine both of these mods on the same switch (double pole, the circuits must be kept 
separate!) you can eliminate one of the switches and simplify operation.  In one position the switch would make 
both the Gardner and Napoli circuits (just as in the factory configuration), in the other position the switch would 
break both circuits (invoking both the Gardner and Napoli mods).  Here is the way this works under the 3 main 
operating modes of the A/C system: 

A/C System Off - The normal factory system configuration includes vacuum solenoid energized (fresh air 
flaps closed), and no power to compressor of course (except late XJ-S convertibles).  If you open the 
combination switch (Gardner and Napoli circuits), vacuum solenoid loses its ground (fresh air flaps open). 
 Napoli circuit has no effect since there is no power to compressor anyway.  If you close the combination 
switch, the vacuum solenoid closes fresh air flaps (just like factory configuration), and makes the Napoli 
circuit (which has no effect since the A/C system is off and no power is available to the compresssor). 

A/C System On - Normal system configuration (except at full cooling) includes vacuum solenoid de-
energized (fresh air flaps open), and power available to compressor.  Opening the combination switch cuts 
power to the compressor (just like the solo Napoli switch), and has no effect on the vacuum solenoid which 
is de-energized anyway (except at full cooling, see below).  Closing the combination switch allows power 
to the compressor, and makes the circuit for the vacuum solenoid (which is de-energized anyway so there 
is no effect). 

 
 

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A/C System in Full Cooling - At full cooling the combination switch will be closed of course, so you’d 
have power to the compressor and the vacuum solenoid energized to close the fresh air flaps for recirc and 
max. cooling. 

“As I said earlier, I’d rather not add another switch which isn’t necessary and which requires additional thought and 
manual intervention (lessee... if I have the Gardner switch closed, should I open the Napoli switch, etc.? )  It seems 
easier to say "I want fresh air only, open the combination switch with the A/C system off" or "I want everything but 
compressor, open the switch with A/C system on." or "I want normal operation, close the switch."” 

 

GARDNER/NAPOLI MOD COMBINATION SWITCH:  John Smith sends this suggestion:  “The interior drivers 
lamp switch, the push on/push off switch next to the interior light switch is - you guessed it - a double pole switch.  
I have seldom used this switch for its intended purpose as it only provides minimal lighting. 

“I removed the switch, and to give it a `genuine` A/c switch appearance I installed the letters`A/c` behind the switch 
window. 

“To do this the switch must be carefully dismantled by drilling out the flaring of the small rivet and removing the 
rivet.  This will allow the small side cover to be removed.  Do this carefully because there are three springs and two 
copper contacts which will be loose inside and you need to note their position for reassembly. 

“This will give access to the switch inner and allow you to gently prise off the front cover revealing the silhouette 
indicator piece of plastic with the lamp emblem.  You will also see three small rectangular opaque plastic light 
diffusers.  If you want a better looking and better lit switch - do not re install these.  I also recoated the inside of the 
poorly painted white areas with liquid paper. 

“On my bubblejet printer, I printed `A/C` using an 18pt Ariel bold font with white print and black background. 

“I carefully scraped away the lamp emblem, leaving a small cleared rectangle to allow enough backlight through for 
the `A/c` label which I glued to the front over the scraped and cleared space.  I sprayed the front with artist’s clear 
fixing spray and reinstalled within the front switch cover and then reassembled the switch.  Make sure you don`t put 
the `A/c` label upside down.  The little red window is at the bottom and the green at the top. 

“When refitting the switch side panel, make sure the hook on the piece of spring wire attached to this panel, engages 
in the in/out white plastic mechanism.  A very small self tapping screw will replace the rivet. 

“Wiring is as follows.  Cut the connector wires about one inch back from the connector.  Put the connector to one 
side.  Get hold of the cut loom wires and join the the purple and the purple/ blue wires together.  Tape off the ends 
of the black wire and the purple/white wire.  These are not positive leads but it is best to tape them out of harm’s 
way. 

“Now the connector.  Prise the connector cover open and relocate the brass terminal loop attached to the purple/blue 
wire from position 7 to position 9 alongside the purple wire.  To check the wiring is correct, attach the connector to 
the switch and make sure there is continuity between the purple and purple/blue, and continuity between the black 
and purple/white when the switch is pushed in to the on position. 

“To complete the wiring, hook up the vacuum (fresh air) wiring to the purple and purple/ blue wires and similarly, 
the A/c clutch wires to the black and purple/white wires.  I soldered the joints and insulated them with heat shrink 
tubing to make a secure neat job. 

“Reinstall the switch and it looks and works in a totally professional way.” 

 

NAPOLI’S MOD TO THE GARDNER MOD (!):  “Instead of wiring the Gardner switch to cut out the ground, 
wire it to apply power to the solenoid.  Then, whenever you want recirc, regardless of the mode the climate control 
system is in, you can get it.  You also preserve full Gardner functionality with the climate control off -- just switch 
off the switch.”  Essentially, the regular Gardner mod switch is OPEN/AUTO, while in this scheme it is 
OPEN/CLOSED -- complete manual control of the recirc flap. 

 
 

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SAWYERS MOD:  The Sawyers mod is really another variation on the Gardner mod, providing improved control 
over the recirc flaps.  It requires a two-pole switch.  Craig Sawyers says it “does exactly what you want.  Position 1, 
recirc under all conditions.  Position 2, fresh air when mode = "off" and normal Delanair operation in any other 
mode switch position.”  Since “normal Delanair operation” means that the system is in fresh air mode nearly all the 
time but will go into recirc mode under the most extreme circumstances, the switch becomes a “fresh air/recirc” 
switch that the system has the capability of overriding when it really needs to in order to maintain temperature 
control. 

“Unplug the pink connector at the solenoid (it has two pink wires going into it), and unplug the servo multi-way 
connector on the opposite side of the car.  Now chomp one of the wires going into the solenoid female spade 
connector, and find out which one of the two wires you now have connects to the pink wire on the servo connector. 
 That is the wire you don't want - the one you do want actually goes to microswitch C in the mode switch assembly, 
which you can't physically get to without dismantling the car.  Note that you actually want a break in the correct 
pink wire - so you might have to resolder the one you just snipped, and snip the other one. 

“Now take your two-pole switch and common up the wiper.  Connect that common point to the vacuum solenoid 
end of the correct broken pink wire.  Connect the NC (or NO) end of one pole to the other end of the pink wire.  
Connect the other NC (or NO) to the brown wire mentioned in my earlier post.  Now plug both spade connections 
back onto the vac solenoid. 

“Here's what the scheme described above looks like electrically: 

 

“In operation, one switch pole interrupts the +12V feed that comes from the mode switch when in the "off" position. 
 It is really identical to the Garder mod but with the switch in a different wire.  The second pole of the switch is used 
to apply +12V to the solenoid when the mode switch is in any other position.  So with both switches open, you get 
no +12V to the solenoid with the system "off", and the solenoid under servo control with the any other mode 
position (Gardner when "off", servo control in any other mode position).  With both switch poles closed, you get 
+12V through the pink wire with the mode "off", and +12V from the brown wire in any other mode switch position 
(recirc no matter what).  Just to complete the description, mode microswitch C takes a fused +12V from the fusebox 
and either connects it to the pink wire when "off" and to the brown wire in any of the other four mode switch 
positions.” 

 

BERNETT MOD:  Tom Bernett explains his mod:  “The Gardner mod opens the fresh air vents with the system 
turned off.  My mod disables the fans and compressor with the system turned on.  So I have fresh air and control of 
cabin temperature using the temp control knob. 

“My mod requires switching open two circuits; one at the Water Valve Temperature Switch, and another at the feed 
to the Water Temperature By-Pass Switch in the servo unit (the brown wire at connector P2 near the servo).”  
Bernett describes how to test this operational mode by merely disconnecting two wires, so you can decide for 
yourself if you like it well enough to go ahead and install a switch: 

1.) Remove the left hand console side casing and the underscuttle casing.  The Water Temperature Switch 
is located above the black footwell vent.  It's attached to a water pipe and has two connectors attached to it. 

 
 

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 One connector has two brown wires, the other has two brown w/ yellow stripe wires.  Undo the connector 
with the brown/yellow wires. 

2.) Remove the right hand console side casing.  Find connector P2.  It's located down low and aft.  It's a 
circular white connector, maybe an inch in diameter with about 10 wires.  Cut the brown wire between the 
connector and the servo unit.  Cut it in the middle so you'll be able to connect to it later.  Careful, don't cut 
the brown/yellow wire by mistake.  You want the solid brown one. 

“That's it.  Try it out.  Turn the ignition on and the mode switch to Auto.  (If you have the Gardner and/or Napoli 
mods, switch those off)  The servo unit should respond to the temp control knob, the blowers and compressor 
should be off, and if you're moving, fresh air, conditioned according to the setting of the temp control knob, will be 
flowing through the dash and footwell vents.  Defrost position on the mode switch should still function. 

“Why it works:  The system is designed such that the heating mode is disabled (no blowers or compressor) until the 
coolant comes up to temperature.  This prevents a blast of cold air in your face when you first start the car on a cold 
morning.  After several minutes of running, the coolant warms up and the system clicks into action.  This is 
controlled by the Water Temperature Switch.  This switch closes when the coolant reaches 40°C/103°F and allows 
the system to operate normally. 

“Now, just as you don't want a blast of cold air in a cold car, you do want a blast of air immediately when you start 
up a car that's been sitting in the sun on a hot day.  This is accomplished by a Water Temp By-pass Switch and some 
fan switches in the servo unit.  These are powered when the system is in cooling mode no matter what the coolant 
temperature is.  So they override the above Water Temperature Switch.  These switches are powered via the brown 
wire at connector P2. 

“So, opening the circuit at the Water Temperature Switch disables the blowers and compressor in heating mode, and 
cutting the brown wire at connector P2 disables the blowers and compressor in cooling mode.  In both modes the 
temp control knob, in-car and ambient temperature sensors, servo motor, fresh air flaps, etc. still function. 

“All that remains is to come up with a convenient way of doing the above switching.  I'm presently operating the 
mod with a double pole toggle switch.  Opening the switch shuts down the blower fans and A/C compressor, but 
still keeps the fresh air flowing and the temperature control knob and servo unit functional.  Close the switch and 
the system goes back to normal operation. 

“I envision using this mod as my on/off switch.  I'll leave the mode switch in Auto, and this switch open in all but 
extreme conditions.  When I need max heat or A/C, I'll close my switch and the system will operate normally with 
both blower fans and A/C compressor.” 

 

 

Delanair MkIII (1987-On) 

 

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.