our 62K mile XJL now thinks that it's freezing cold outside, so the A/C barely works because the car thinks it isn't needed at all. No temp control or blower functions, just a baby breath of cool air. The dashboard icon shows a big snowflake.

Our local mechanic (nice guy, not a Jag expert) thought it was a sensor, and now thinks it's the whole control panel. Since the dealer is over an hour away, what would you experts do in order to diagnose further? More to the point, if a control panel is needed, this sounds like MegaBucks, so is there a workaround?

 

Did the local shop check the refrigerant level in the system as part of their inspection?

 

I don't know what they did; my boys picked up the car, but I'll ask him tomorrow when I settle up his bill with him. Thanks!

 

Update; I tested the battery in the car and it reads 12.11V, which seems low to me. Battery is 4 years old. Could a battery with lower voltage trigger such a fault as we're having with the A/C?

 

The battery should be charged for four or five hours at 2 to 5 amps and retested. There should be a minimum of 12.6 volts across the terminals with the ignition OFF when tested with a voltmeter. If there's still less than 12.6 volts, the battery is suspect and should be replaced.

Low available voltage can cause random faults, but any further diagnosis should be performed only with a fully charged battery.

 

10-4, I'll put the charger on it. Car sits for days at a time between runs, sometimes a week or two, and now that I'm thinking about it, the trips it takes are 10-minute runs which won't fully charge the battery. memo to self is to check that battery condition every month or two. Thanks for the tip.

 

If your battery checks out. The snow flake on the dash usually indicated an outside temperature that is close to freezing. Is there a chance your outside air temperature sensor is bad? What temperature does the car say it is outside?
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The battery is at 12.72V, refrigerant is correct, and temp readings are correct, I just have no control over setting the temp or fan speed. My indi says he did research and it is pointing to the control panel computer. He can't source one because it needs to be programmed by a Jag dealer, so a used one is out of the question, too. Seems that that's a $1,700 part, not counting labor.
What's odd is that there is A/C in the car. Very little blowing, but the air is cool enough that we're comfortable, so at least the car is driveable.

I wonder if there's an alternative to taking it to the dealer? The drive over to Mobile is not an easy one for my wife to follow me because she's scared to death of going through that tunnel.

 

UPDATE: I just went to Pensacola and back (a 2 hour trip). Control panel read 86 degrees outside, which is accurate. No temp readings for the interior, despite the A/C being ON and cooling the car like normal. Can we deduce that the temp sensor in the bumper is operating as it should/reading correct ambient temp? That's pointing to the processing unit as the culprit, although I've no idea why it's telling the A/C to operate even though it thinks that the outside temp is below freezing?

 

Yes I think the outside temperature sensor is working correctly. I was hoping for an easy and cheap fix but maybe not? Just to let you know Jaguar has moved it from under the hood in the center of the car to one of the side mirrors.
I know your using an independent but with what you have posted I again must recommend getting the car hooked to a SDD and reporting back to the forum.

Now your mechanic is sorta right and sorta wrong about the module replacement? Yes it will most likely need programmed to your car and yes from Jaguar's point of view this can ONLY be done using a new module from them. As you found out this will be an EXTREMELY expensive repair. If you can find a shop that is using SDD they usually can reprogram a used module by telling SDD that's it's new module and needs to be programmed. Now I need to be careful here as we don't know exactly what part we are talking about yet?

If you can get a part number or a more detailed description we might be of more help too? Remember we might have a bad module or we might be feeding the module bad information. We don't know at this point.

One guess is from my earlier Jaguar which was a S-Type. Those cars had internal evaporator temperature sensors and there was 4 of them because of the dual temperature control system. I had a failure of one of them but with much different symptoms from you so probably not your problem. These sensors again can be checked by the SDD system.

After thinking some more I also have had problems with a different part and that matches you symptoms much better? I should have keyed on this earlier so sorry about that! There is an interior air temperature sensor behind a grill right above the push start button. There is only one of these so it affects everything temperature wise. Your cooling is unaffected so this maybe wrong too?

I have circled it in red below. The other red circle is a small flap that is covering a mounting screw. If I remember right remove that one screw and the panel snaps out.




What happens is the temperature sensor has interior air blowing over it 100% of the time. Over time the sensor can get a build up which affects the temperature reading. Since you have no interior temperature reading at all maybe this sensor is disconnected or has failed? Or it's working but has failed to put out the signal driving the temperature display?




Surprisingly this is only about $60 new? Part number AW93-8B506-AB on the part sticker but I think the correct part number is C2Z5465. Careful as I am seeing used parts costing the same as a new one. Now this is not a failure prone part so if you do find a used one for a good price I would take a chance and get it.
Interior Temperature Sensor

I hate to recommend throwing parts at it but it seems so hard to find a good shop using SDD that you "might" consider just changing that internal temperature sensor as a hail Mary pass?
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Great write-up!! My indi is a general mechanic with a 4-person shop, and just looks at my odd-ball cars because we talk boats and such. He is also around the corner, rather than a long drive to the dealer. There is another shop that is a specialty shop and they're much closer, so I'll ask them if they have the equipment to both diagnose and...if needed...program replaced items.

Agreed that throwing a $60 part at the problem is a calculated risk with no down-side potential since the cost is negligible.

Now to make an appointment with the specialty shop. As luck would have it, they are the only shop like that within a large area, so wait times are measured in weeks at a minimum. Thanks for the counsel.

 

grrrr, that lower retaining screw is neither fun nor easy! Why'd I choose a no-wind, 93 degree day to do this??

The good news is the there's one on eBay for $38, and it will be here Friday!

 

Too hot in the garage to do much more tonight, but seems that another piece of dash needs to be removed. The plug for the sensor isn't wanting to come into view, and if I yank it....well, you don't yank on electrical plugs because you'll not be able to get the new one attached....so is there another process? It's tight up in there.

 

It looks like the driver's side of the center console panel needs to come off. If that is correct, what's the drill to remove, or do I go through the display screen console?

 

I was installing my Android screen so I did remove the entire console and the side panels for that as I had to run cables from the front screen back into the center console storage box for an external USB port. The side panels just pop off and you can leave them in place but they are under another piece of trim that does have bolts. I never removed the sensor your working on so no help with that. But here is a picture from the shop manual that might help? It only shows 2 screws and an electrical plug holding the air temperature sensor in. Note I believe this is showing a RHD car after looking at the layout of the panels and sensor location.



It's been a while so I have forgotten some things too? But the back of the panel I posted a picture of just shows one screw and then all clips? I think after removing the screw it should pull straight out? Take a look.




Your getting deeper than I did too so your in new territory!
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Removing the display screen is a Must, because the sensor's connector (magenta color in your photo above)is attached to the radio compartment wall. You can't remove the sensor without cutting those two white plugs off from inside the radio compartment, then there isn't enough free play in the wiring to allow access to the connector, so I'm going to have to remove the side panel on the driver's side, too.

This is like you wanted to spend an hour changing spark plugs, only to learn that the rear plugs can only be accessed by removing half of the engine compartment!!

 

Update: There's a cutout behind the lower box that should allow me to make the connector swap, so removing any of the center console is not needed.

 

Here are the two plugs that retain the sensor to the radio side-wall

 

Thanks so much for the pictures! Your breaking new ground for me. Let's hope the sensor is your problem because this is still a guess at this point without any codes to guide us.
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always happy to contribute when we can!. The old sensor has a tiny fan that draws air over the sensing disc, and there was accumulated dust on the blades, just as there would be on your bathroom fan. I blew off the dust and plugged back in, but nothing changed. If the new one fixes things, fantastic, and if it doesn't, we go to the dealer, but it's good to learn things and....so far, nothing broken or lost!

BTW, there is no earthly reason why the connector needs to be firmly attached to the sidewall, and it would be PITA to try to re-attach per OEM. It will be left inside that closed space and won't interfere with anything.