Mechanics

STRANGE FAULT WITH HEATER/AIRCON

2002 Jaguar XJ8

Air Conditioning problem
2002 Jaguar XJ8 V8 Two Wheel Drive Automatic 40000 miles

With the aiircon on auto, set at 70deg after around 30 mins of driving the fan speed increases to max and only cold air flows, before that it seems ok.

Changing any of the controls does not fix the problem. You can hear a series of clicks from what sounds to come from the central vents, it sounds like the fllap servo motor gear is running on too long.

These clicks even continue after the heater/aircon is turned off.

If the engine is turned off and left to cool the heater/aircon returns to normal (for the next 30 minutes).

My theory is that after around 30 mins the climate system need to cool the car and some sensor is not working correctly and the cooling and the fan are set to max.
I have run the diagnostics and it is showing failues of left, center and right vent servo motors. It seems unlikey that all three servos have a problem.
Any ideas of where the problem may lie or any other tests I could do to track it down.
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Greenacres
February 28, 2009.




Hello .. thanks for the donation .. much appreciated

This sounds from your description, like you have a fault on the Motorized In-car Aspirator ... my manual does not supply any test procedure for this unit !!
you could try disconnecting the wires and see if you get the same symptoms ? hope this helps .. let me know !

Motorized In-car Aspirator
An intake grille (mounted on the fascia, outboard of the steering column and below the EOD vent) houses the aspirator thermister. The remotely mounted motor / fan assembly draws cabin air through the grille and thus over the thermistor; a flexible hose connects both components.
The electrical resistance of the thermistor changes in response to variations in air temperature, this change being converted into an electrical signal. The A/CCM uses this signal to adjust the temperature, airflow and air distribution from the air conditioning unit.


http://www.2carpros.com/forum/automotive_pictures/266999_asp_1.jpg


11 Motorized in-car aspirator malfunction
Possible Source(s):
Harness/connector fault
Sensor open/short circuit
Action(s) to take:
Panel fault codes are not stored for motorized in-car aspirator motor failure.


http://www.2carpros.com/forum/automotive_pictures/266999_asp2_1.jpg



http://www.2carpros.com/forum/automotive_pictures/266999_asp3_1.jpg


Dave H
Mar 1, 2009.
Hi Dave, thanks for the response.
I could not work out what the normal levels of donations are!

I removed the Motorized in-car aspirator and tested it, the small fan runs and the termistor's resistance changes when you warm it.

When running the engine with the aspirator removed it seems to operate as normal but perhaps not as good at regulating the temp, as you would expect.

With the engine running (and warm) I tried cooling and heating the aspirator's termistor and the system reacted to that as expected. Also I did not see the failure having waiting 30 mins but perhaps it does not show with the car stationary or perhaps I did not quite leave it long enough.

So I'm thinking that's not the problem.

I re-ran the inbuilt diagnostics, at first you get code 0 (no error) and the fan them starts to speed up (sometimes to full speed during the diagnostic cycles) and after 20-30 seconds I get one error code, then after another 10 seconds another and then sometimes a third. These are all active as they have bleeps.

When I reapeat the diags I get the same sequence except the error codes have some differences; Try 1
Code 0 then after 30 sec code 14, then code 43, then code 46. 14, 43 & 46 then cycle.
Try 2
Code 0 then after 30 sec code 43, then code 45. 43 and 46 then cycle.
Try3
Code 0 then after 30 sec code 43, then code 45
Try 4
Code 0 then after 30 sec code 14, then code 44

I tried the actuactor test sequence (20-27) but that did not change anything.

After a few diag cycles the errors were; 43(Cool Air By-Pass Servo Motor, 11 times)
34(Defrost Vent Feedback Potentiometer, once)
14 (? Twice)
44(Defrost Servo Motor, twice)
45(Defrost Vent Feedback Potentiometer, once)
46(Foot Servo Motor, once)

I keep thinking back to the sound when I get a failure, which is like the center servo motor running but the A/CCM not reading the flap potentiometer correctly and it keeps driving the servo and the gears just click over at their end stop. But if that was the case I assume that I would see a 'Center Vent Feedback Potentiometer' failure code. I am assuming that Jag designed the system so that the flaps would not hit the end stops and then keep clicking!

However your answer seemed to fit well.

If you were working in this car what would you try or do next?

Many thanks.

Tiny
Greenacres
Mar 1, 2009.
Hello. There is no set donation. You give what you think the service we provide is worth to you. Any donation is a bonus and gladly recieved. Thank you

I would now be looking at the cool air by pass motor as this seems to be the main fault code coming up? I would also have the vehicle scanned by jaguars PDU to see if that actually gives me the exact fault? Let me know

14 Water temperature input malfunction
Possible Source(s): Instrument cluster output
Action(s) to take: Refer to PDU

34 Defrost vent potentiometer fault
Possible Source(s): Harness/connector fault
In certain circumstances the servo motor may over-travel and cause further logged faults. This may be cured, following fault rectification, by cycling the ignition ON-OFF-ON 3 times

43 Cool air by-pass motor fault
Possible Source(s): Harness/connector fault
Servo motor seized or sticking
Flap seized or sticking
Action(s) to take: Refer to PDU

43 Cool Air by-pass motor fault
Possible Source(s): Harness/connector fault
Servo motor seized or sticking
Flap seized or sticking
Action(s) to take: Refer to PDU

44 Defrost vent motor fault
Possible Source(s): Harness/connector fault
Servo motor seized or sticking
Flap seized or sticking
Action(s) to take: Refer to PDU

45 Centre vent motor fault
Possible Source(s): Harness/connector fault
Servo motor seized or sticking
Flap seized or sticking
Action(s) to take: Refer to PDU

46 Foot vent motor fault
Possible Source(s): Harness/connector fault
Servo motor seized or sticking
Flap seized or sticking
Action(s) to take: Refer to PDU
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Dave H
Mar 1, 2009.
Many Thanks

I'll book it in an see what the PDU says.

Tiny
Greenacres
Mar 1, 2009.
Some systems on HVAC do not throw out a fault code on the self test. So it could be on one of these systems/sensors and we could be looking in totally the wrong place. Let me know how you do !

Dave H
Mar 1, 2009.
Hi Dave

I had the car checked with a PDU and it threw up codes; B1268
B1264
B1263
B1266
B1267

Which all seem to be flap feedback potentiometers.

The garage want to change the control unit and all the servo/flaps which I think will be expensive and not the right solution.

I have seen that when you get one error (from the panel diagnostics) then some time later you tend to get a lot more errors.

I suspect that either the cool air bypass flap servo or it's potentiometer or maybe the physical flap is catching somehwere.

Other than that I suppose it could a problem with a common power supply for all the potentiometers which is failing after a period of time or when warm etc.

Anyway thanks for your help.

I did get hold of a. Pdf copy of " SERVICE TRAINING COURSE 703 JAGUAR CLIMATE CONTROL SYSTEMS" which helped explain the system, but not my particular fault.

Tiny
Greenacres
Mar 10, 2009.

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