Heating

[almcl]

Pop

You raise an interesting point.

I've yet to find two people who agree about what the auto function of the climate control is supposed to do and how it should do it.

My understanding (far from perfect) is that in auto, the Mk III system should try to maintain a constant cabin temperature, regardless of outside conditions. Moving the temp knob should vary this up or down. Moving the center knob will vary the face level temperature but still within the bounds of what the temp control is trying to achieve.

How this should be achieved seems to be less well described but again my understanding is that the system can vary the fan speed, open or close the recirc flaps, open or close the centre vent and vary the blend flap in an almost infinite range of steps to achieve its commanded settings.

From the posts here and elsewhere, it sounds as though this isn't a universally held opinion, though.

[dhdove]

Dear All

Thought I'd throw in my threepenneth worth............

Again my understanding of the system is not great......... but I believe that in auto mode the system will take account of the cabin temp sensor and constantly adjust the cabin temp in accordance to the temp. set on the control dial.
In manual mode it will ignore the temp sensor and just keep on blasting out what you have dialled in ie if you set it to hot it will keep on blasting out hot air for as long as it's turned on and similarly for cold. What it does in between I'm not sure...........

Having owned four xjs's I CAN say that none of the air-con systems worked as advertised, the nearest was my last car, an '89 3.6 Coupe............but then I poured nearly a thousand pounds into that system........

For now I'm more than happy that when I select hot I get hot, ditto cold, the fans work on all speeds and it demists efficiently Manual fine tuning works on the window button............

NB I did suggest to Nigel Thorley a couple of years ago that the Club should run a seminar on air-con, but he thought it was too specialist a subject and wouldn't get the neccesary support.......

Best Wishes

DH Dove

[Mark_B]

Oh!. It might well be I have the only working climate control here!

Mine works perfectly. On manual, starting from centre setting you can vary the air blow from the vents from nothing, to increasing heating effect while turing knob clockwise, starting from luke warm to ouch! and with all shades in between. Turn it the other way from centre starts off with nothing, to increasingly cooler, ending up with icy. The further away from centre setting, the faster the air blows out. When blowing cold, the centre vent opens. Once when the centre vent actuator failed, the cooling effect was still present to some extent, just not very good.

As it's a proportional control system, the heating/cooling effect has to have a linear response to the knob setting, otherwise when in auto it can't control properly (like non-linear steering effect).

Set mine to auto and forget it. Stabilises cabin temperature within 0.1 degree. Vary the red/blue 'air' swivel thing from red to blue and the cabin temp stays the same but get hot feet and cold face, nice when icy day with sunshine.

When that kind of system goes wrong, without full detailed symptoms it's hard to make an educated guess what could be wrong.

[dhdove]

Mark

Sorry to be a thicko but.........when you say in manual mode "starting from centre setting" do you mean temp knob in the horizontal? If so, where is the fan knob set to? How does the blower power vary if it's in manual mode?

I really do think that this is a subject that we would all benefit from some informed education and tuition - despite what Nigel says!

Regards

DH Dove

[phil235]

Hi Everyone

Thank you all for your thoughts I am working my way through the system and I will report if I come up with any results.
Any further help is wellcome.

Thanks Phil

[Mark_B]

How does the blower power vary if it's in manual mode?

When right knob set normal, left knob out (manual), left knob set horozontal, the air speed is the lowest, almost nothing.

When left turn knob away from horizontal the fan speeds pick up.

The air blending inside varies the temperature as well as the air speed, the net effect is increasing heat/ cool depending on knob setting.

Unless this works ok, it won't work very well at all when set to auto.

[q

[ptjs1]

Phil,

As you've probably realised, you have the latest XJS system which has completely different controls and operates in quite a different way to the earlier systems to which most people are referring.

Drop me an email and I'll forward you copies of some of the explanatory and diagnostic pages from Jaguar.

Just as a suggestion, your system has three temp sensors monitoring Exterior ambient temp, In-car temp and Evaporator temp. In Auto mode, the temp is thermostatically controlled by reference to the temp signals passed to the control module. (Auto mode also controls fan speed and distribution.) In Manual mode, it fixes the temp (and fan speed) based on the position of the temp dial (and fan speed dial) and doesn't try and use the sensor signals to determine how to vary the temperature. Therefore, my limited understanding of the system says that if you can't get heat in Auto mode but can in Manual mode, then you would perhaps look first to a failure in the in-Car temp sensor?

As I said, drop me an email.

Paul

[phil235]

Hi Everyone

I have checked the heating and I am getting warm air from top vents + demist when set and warm air from side vents. Nothing from center vents and only cold air on any heat setting from lower vents.
Do you think it is a stuck centre vent flap which is stopping the warm air from coming out of the lower vents.

Thanks Phil

[almcl]

If you have heat to the upper areas but not to the lower, then the lower flap is not moving. It may be stuck, or its actuator may not be moving. Worth investigating with the cheek panels removed...

[kevinhafner]

I knwow the earlier systems ( pre heating ecu) had a very old fashioned fault finding box that could tell the engineer what wasn't working through a series of elimination tests.
Is there such a thing for the delenair III system that maybe plugs into the ecu behind the footwell panel and if so does anyone know of anyone with one?
I have had heating and air con problems posted in air con ' facia vent not working' but have yet to find a specialist in the south east in this field.

[phil235]

Hi Kevin

Had a look in the foot well at the ECU but could not see a plug to fit a line in.

Thanks Phil

[ptjs1]

Phil,

I think maybe Kevin is referring to the OBDII plug-in point that is mounted on the lower A-post by the bonnet release. I don't know if you can interrogate the later air-con system via this point. I'll ring up a friendly independent and see if they know.

Paul

[kevinhafner]

thanks Paul, there has to be an easier way.... doesn't there?!!?

[ptjs1]

Phil,

Don't know if you've resolved the problems. I wonder if you have a temp control problem if you can't get cold air (or a gassing problem). However, the centre vents are not supposed to pass hot air. They only blow air when the temp setting is "cold". However, the end vents will blow air whatever the temp setting.

Hope that helps

Paul

[phil235]

Hi Paul

Thanks for you reply, have not got it working fully yet. I only get a very small amount of cold air from the centre vents at any fan or temp setting. I also only get cold air from the bottom vents but warm from the side face vents. The air temp can be controlled with the temp control but not the bottom vent. When I bought the car last year the air con did not work, so I had it checked fopr leaks and regassed and it works OK now. The auto setting for heating and cooling produces various temperatures usually too warm from side vents but not from bottom vents which still remain cold.

Regards Phil