Role of coolant in my sporadic climate control problem?

[blackflash]

Please see my question posted Mon 26 Nov 07 in the climate control section... Car is now booked into main dealer on Friday, so any help in avoiding or minimising their costly attention would be VERY VERY much appreciated.

Service person booking me in asked whether my coolant level was ok to which I replied yes. I then checked and put maybe a half-pint in to top up but would guess this was not the cause of the problem.

Basically I don't know how the engine cooling system provides the heating to the inside of the car. If anyone knows why my climate control should be misbehaving (and blowing in cool air) most BUT NOT ALL of the time then I'd be keen to understand.

Many thanks,

Nigel

[Brakebuster]

there are two ( three ) types of car ventilation/heating

1, non aircon / heating and ventilation

2, aircon / heating and ventilation

3, climate control = fully auto aircon plus heating and ventilation

aircon only cars ( no auto button ) will be on or off, so if you put the aircon on, it will keep chucking out cold air till you freeze to death ( providing everything is working fine )

climate control cars use the aircon and heating ventilation to maintain the set temperature within the vehicle, the ' sun ' sensor and cabin temp sensors inform the ecu which then decided how to heat/cool the car, that might be the thing here, auto will not always pump out hot air , it will ,once the preset temperature has been achieved put out some tepid/cold air to maintain the temperature set,

this may mean its working fine ??

i have also noted in my own 1999 xj8 sov that i can get warm air out of the screen vents and foot vents while at the same time get cool air from the face vents , this all depend on how you set it up on the dash ,

the heater matrix inside the car ( behind the stereo position ) passes the engine coolant through it once hot ( controlled by a thermostat ), the air taken in from outside passes through this matrix warming it as it goes through , assisted by a multi-speed fan , if cool air is required the air is passed over the refrigerant matrix from the aircon system , thus cooling it , the compressor in the engine bay provided the coolant system power ( like a domestic fridge )

climate control combines these two systems to maintain the internally set temperature,

if you set the air intake to recirculate the internal air, it manages the temperature more easily , as you are not introducing cold (or hot ) air from outside, however some peeps find that the dryness of the aircon air is uncomfortable ( but not me )

oh, another thing to remember is that hot and cold air can be ' air-conditioned ' it simply removes the moisture content

its a bit involved and more complicated than this, but that's the basics

HOWEVER , none of this doesn't mean that you MAY have a problem that needs sorting.............

hope it helps

Vince BB

[blackflash]

Thanks for extensive reply, BB.

I have climate control and am used to how it works (usually excellent) but something has changed and is not right. It appears that the brain thinks it is drawing in air from the heating matrix but actually drawing it on from the refrigerant matrix. Recirculation makes no difference.

I'm interested in the "sun" sensor as I thought it was only a cabin sensor which got involved (and I recently replaced my internal photochromic mirror - if this is where the sun sensor is, then I have a clue...).

However, the fan speed increases/decreases as you'd expect which is why I think (a) it is detecting ok, (b) the brain is doing the right calcs, but (c) it is most of the time drawing in cooler air than it thinks it is.

Tell me I'm wrong if so. Great to have someone to bounce this off!

Nigel

[Brakebuster]

right,

the ' sun ' sensor is the small black plastic bubble on the top of the dash in the middle between the screen vents , it detects ' sunlight ' to tell the ecu if the car is being warmed by the sun, simple as that really,

if your used to climate control, then thats half the battle, its surprising how many are confused by it , and the differences to aircon

this is only a stab in the dark suggestion, if you think the ecu is not behaving correctly , then arm yourself with your stereo code and disconnect the battery in the boot for half an hour, but first ensure that the key fits and opens the boot manually, and that if possible you leave the boot open anyway , and dont lock the keys in the boot, as your into drilling holes behind the number plate,

this may just ( may! ) reset all the info in the ecu , this will not effect any of your systems at all, just clear fault codes and any miss behaving items , if it works, its a lot cheaper than Jag doing the same thing, and saying they fixed it.....

however, it may well be the motor driving the flow direction between the to matrix units, it may be faulty, intermittent , or just confused for some reason...

ask away anytime,

BB

[blackflash]

Nice one, BB. So that's what the bubble is...

If my day goes as planned tomorrow then I'll try this in the early afternoon so if it works I'll have time to cancel the main dealer appointment.

I know I'll need the radio code and the clock will need resetting - I assume memory seat settings etc are unaffected by disconnecting the battery.

Will keep you posted,

Nigel

[joejag308]

No posts for almost a year, so it must be a good topic, but its coming to THAT time of year guys so prepare for the worst.........Joe.