I just purchased a 97 XJ6VP with 35000 miles. The car is beautiful being garaged from new. I drove it about 500 miles home yesterday with absolutely no issues. One concern is the volume of air coming out the center air vent when I have the button pressed for face level. The AC was ice cold but for a minute or two, the volume of air out the vent was forceful but then would suddenly cut back even though the fan motors continued to run at the same speed. On my 95, if I choose the same setting, it will give me the same volume of air until I manually turn the fans down.

Any help sincerely appreciated.

Richard

 

There is a built in self test that will display numbers like CEL's by a Jaguar TSB . Look at the panel code column # for correlation . Recommend doing the self test and clearing the codes as some may have latched years ago as a hiccup and if the fault reaccures then do a fresh self test for present code #

http://www.mediafire.com/file/b38zz8...System+DTC.pdf

 

I did the self-test but no codes showing. Playing with it more, if I press one of the other buttons such as "face/footwell" and press the "face" button again, I get full face volume for about a minute then back to maybe half. It seems like the vent is fully open and then closes partically????????

 

Sounds like the Climate Control ECU drives the trim motor to it's correct commanded position and the feedback loop back to the ECU agrees hence no code . The monitoring is satisfied and shuts down ( by design ? ) and later the valve physically moves hence the change in temps . This valve movement in my opinion is probably a command from the ECU that is in error .

Both the valves and the ECU ( easier ) are not straight fwd to get to and someone else my have a suggestion

 

Not meaning to hijack the original post, but perhaps related...

.... what effect does anyone notice when adjusting the temperature thumb wheel in the middle of the center vent? This is the vertical thumb wheel that has the blue and red dots and in theory changes the temperature of the air from the center vent independently of the main controls.

Mine doesn't seem to make any noticeable difference in air temperature when the thumb wheel is moved to full hot, center or full cold. I haven't put an IR temperature sensor on it, but my analog hand test doesn't notice any significant change.

In contrast my friend's BMW has a similar feature, and the temperature changes dramatically when the wheel is adjusted.

So what is your experience on the X300?

And, if my experience is abnormal... that is, it should make a noticeable difference, what might be the problem?

I know it is properly hooked to the harness, but beyond that I don't know the mechanism it uses to manipulate the air temp coming out of the center vent.

.

 

Researching what Al Roethlisberger said as this is a valid point in how the plenum trims the outflow temp to maintain the the set cabin temp . There are other direction valves that direct the flow from foot to defrost and such . The temp trim fine tuning would be a short time " shot " of command voltage in one direction or the other and would tune the physical position somewhere between full open and full close and not hitting the agreement switch . It probably hits the switches as you first turn on the system on and then proceeds to trim as it tries to agree with the cabin temp sensor located on the very left side of the left kick panel on a LWD car that has the louvers on it . Mine was very dirty and clogged and cleans up well . I cleaned alot of these in the cockpits and cabins ( as they were trimmed separately ) of the airliners .

Al , is this constant adjusting trim shot also going on with the heater pump valve to maintain the cabin temp at a level setting ?

 

Apologies, but not really following your post above

..... so the weather has now had some cold snaps here, and I've had a chance to try moving the thumb wheel with the heat on, and still didn't notice any change in temperature coming out of the center vent.

Again, is this typical, or is mine just not working?

And if it should work, what is actually happening when it does? Is it just triggering a damper,or?

.

 

Page 45 of 230 is a manual on the XJ Climate Control that may or may not cover the X300 as the X308 is the same if not similar .

I'll be back later

http://www.jagrepair.com/images/Trai...des/703_SG.pdf

 

Thanks, unfortunately the X308 doesn't have the same center vent with the thumb-wheel to manually change the temperature. The X308 had a clock in that spot So this manual doesn't seem to cover this issue.


Also, again, does this switch work on anyone's and make any noticeable temperature difference?


Just in case there is any confusion, this is the "thumb wheel" switch I'm talking about:

 

Lady P. is behind the curve right now so I can't run her until i get the downpipe back but I did find this on the print .

 

Parker's link does cover the X300 system, and surprisingly, it is the same as the X300 save the wheel (notwithstanding the underhood components)

"OVERVIEW
The Jaguar Denso Climate Control System, introduced in the 1995 Model Year XJ, is standard equipment on XJ and
XK models."

I failed to weigh-in when Al first posed the question, because it has been quite awhile since I read the manual, but a review of Parker's link reaffirmed my memory of what I'd read long ago: The wheel tempers the center vent discharge air relative to what is coming out of the foot vents. Yes, in mine (when the heater is working,) I notice a difference. It controls the position of the bypass air flap. See diagrams on 2.5.8 in Parker's link above.

 

To test the Differential Control Potentiometer you can remove the CC31 connector on the A/C ECU and read a resistance change as you move the thumb wheel . An open is a bad Potentiometer

CC31 - 8 wire color Purple

CC31 - 19 wire color Black / White

CC31 - 22 is a empty socket so it is a connector identifier as the other 3 connectors have a wire occupying the 4 corners of the other connectors .

CC28 - 13 wire color Blue / Orange

CC28 - 26 wire color Green / Blue

Will drive the Cooling Air Bypass Servo open or close . Works with a 9 volt battery , you can hear it run

CC29 - 5 wire color Slate / Blue

CC31 - 19 wire color Black / White

Will read the servos position which is needed in the adjustment system follow up

 

Back to the original question , it my be that one of the potentiometers brushs are lifting off the windings causing the servo to drive closed with a higher airflow resistance through the heater core or matrix resulting in decreased vent airflow rate .

Potentiometer replacement ? hard

Or drive the servo with a pigtail wire you can easily get to to drive to the closed position in cool outdoor temps and open position during hot outdoor temps . Electrically isolate the servo after movement , assuming the servo doesn't creep to a different position .

Physically what is happening in the heater operation is this control reduces the harshness of the vents output hot air . In the cooling operation it just restricts the airflow and may be commanded to the full open position once the A/C mode is turned on regardless of the position of the thumbwheel . By it wondering in this example points to a bad servo position potentiometer . With the servo in the open position reading low resistance my head hurts

I could be wrong .

I will have to verify the correct tap on the winding is used so the ring out chart agrees

You may not see the potentiometer fail as it may be temperature dependent

 

Great information! Gives me a starting point to see what is or isn't working properly!

.

 

Apologies for the delayed feedback, but I've just gotten around to testing the bypass flap and dash vent potentiometer based on the information above, and I can report that it is exactly what was detailed.

I was able to measure the impedance of the pot, and it was good after I cleaned it with some contact cleaner.

I was able to put 9V on the bypass flap via wires 13 & 26 on connector CC28 and with reversing the voltage was able to hear the flap actuate back and forth.

After putting it all back together I could now hear the bypass flap actuating as I moved the potentiometer back and forth between the "red" and "blue" dots.

It is interesting to note that when the climate control is set to blow on "face" only, the bypass flap doesn't move. But on any other setting it does.

Now, all that being said, I still didn't really notice any significant difference in air temperature when the bypass setting was changed, but this may be because I am running heat even at the lowest temperature setting this time of year. This may make more of a difference during seasons where the temperature is warmer and the A/C is cooling? Not sure. We'll see.

Thanks again for the information!

 

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