Experience in a Book
Air Conditioner/Heater Mods

Modifying the climate control system? Actually, this section describes a couple of the most popular modifications to the XJ-S. Referred to as the Gardner/Napoli mods after the guys who described them in detail on the Internet discussion list, they provide an increased level of control in a system that seems designed for as little control as possible. It should be noted that these mods are described as they apply to the early system, and may not apply to the Delanair MkIII system. They also may not be needed in later cars, since the later systems provide more control to begin with.

NAPOLI MOD: The idea of this mod is simple enough: provide a switch to enable operating the climate control system without the compressor when cooling is not needed. John Napoli says, "You are basically adding a switch in series to the inline fuse for the compressor located on the transmission tunnel near the air flap linkages." The wire in question is a GN wire.

Note that operating with the compressor off will not only result in no cooling, but will eliminate the ability to dehumidify as well. In high humidity situations, you will probably need to turn the compressor back on to prevent window fogging and other humidity problems. You will definitely need it on if you use "defrost" mode to clear condensation on the windshield.

Also note that operation of the system in hot weather with the compressor off might cause the "Auto" mode to increase fan speeds, since it's trying to cool and the servo is moving to ever more powerful cooling modes to try to lower the temperature. However, normally the occupants will want to switch the compressor on long before this happens. Even if it did happen, it's simple enough to switch to "Low" fan speed.

There is a fuel cooler in the freon circuit, and shutting off the compressor will obviously result in a loss of fuel cooling. According to Roger Bywater, "the fuel cooler was added as an emission device, not because of fuel handling difficulties like vapour lock, although this could happen on early cars before the fuel rail temperature sensor was introduced. The high underbonnet temperatures of the V12 always resulted in a lot of heat being transferred to the tank with the recirculating fuel and I recall measuring over 60 degrees C at the tank which means a lot of vapour can be given off. To pass a full EPA emission test for certification there are strict limits on the evaporative emissions of the whole vehicle (including adhesives, plastic mouldings, paint, etc.) and the fuel cooler eased this situation by reducing fuel vapour loss. This is why all cars for the USA market had air conditioning - they were not certified for sale without it. Also the convertible would have to have the compressor running continually because the air con would probably not be used with the top down." Hence, the Napoli mod might technically be considered detrimental to the emissions control systems of the car. Note, however, that you would normally only switch the compressor off on days where the weather was cool anyway; presumably, the fuel needs cooling the most on the same days that you do, when you will have the compressor on.

The guys who have computers in their cars report that shutting off the compressor results in an instant fuel economy increase along the order of 2 mpg. As always, your mileage may vary, and in this case some of that benefit may deteriorate as the fuel in the tank gets warmer; warm fuel hurts engine efficiency. And if you roll the windows 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 in Air Conditioner/Heater.

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 (driver's side footwell on LHD cars), 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."

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).

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.

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

93.5-96 JLM11696
92-93 JLM11355
Pre-92 JLM11108

On to Stereo Modifications