Xantia heater cooling down

Panjandrum · Post by **Panjandrum** » 08 Dec 2004, 18:29

Off I go, up the motorway on a freezing day. Slider set to about 22 degrees. Warmed up nicely. Then it begins to get colder. Up to 24 degrees. Warmed up nicely. Then it begins to get colder. Up to 26 degrees.... In the end I was just keeping warm with the temperature set to max. Makes no difference with aircon on or off.
It seems that the further I go the more that something or other overestimates how warm I am.
Now it could just be that I need more heat the longer I sit, but really I don't think so.
It has always been this way, a little, but I was reminded forcibly on a 150 mile round trip on freezing Monday - and I have never had to go all the way to the hottest setting before.
Temperature gauge sitting just below horizontal, where it always sits.
Any suggestions?
Do they all do this?
Is it an intelligent feature to help prevent driver fatigue?
PJ

pete_wood_uk · Post by **pete_wood_uk** » 08 Dec 2004, 18:36

Is the little fan going around that lives just behind the pushbuttons under the air vents on the dash? I think it has that little fan to draw air in over the temperature sensor (unlike the sensible old CX that just stuck it out in the middle of the ceiling under a cage). It striks me that if that fan failed, then the sensor would read the temperature of the dashboard as ambient, and as that warmed up (due to the heater, radio, what have you) then it would give exactly the symptoms you describe.
This is just a guess based on no knowledge. My fans are intermittently noisy, but still working, so I haven't yet een forced to take the dash apart to revive them.
Cheers
Pete

Robin · Post by **Robin** » 08 Dec 2004, 18:40

PJ I would go along with Pete on this one. The fan can also get clogged up with dust etc. Just prise it out and give it a good clean up and a drop of very light oil. Assuming it is working at all of course! R.

Panjandrum · Post by **Panjandrum** » 08 Dec 2004, 18:43

Pete,
Good point. But I am pretty sure that the little inky-dinky fan is alive and well. It was doing some buzzing a while ago and responded kindly to a good blow.
In any case, the heater will do a grand job of responding to different slider positions on my normal slow journey to work. It will blow really quite warm until it gets to pleasant, then sustain that - which seems (to me) to suggest that the fan is fine.
PJ

pete_wood_uk · Post by **pete_wood_uk** » 08 Dec 2004, 18:47

It was just a guess. I suspect that you could rule my theory out completely by getting the cabin good and warm, then moving the slider down to 18 and checking that the car cools down again. If that works, then the fan *must* be working, I think, as must also the stepper motor and lots of the other gubbins in the heater.
Cheers
Pete

Kowalski · Post by **Kowalski** » 08 Dec 2004, 18:59

Mine does similar sorts of things, that little fan in mine is intermittently noisy too.
Let me know how you get on, you can probably find out how difficult fixing mine is going to be for me when you fix yours.

Panjandrum · Post by **Panjandrum** » 08 Dec 2004, 21:01

Yep. Cooling down works fine, with or without aircon on.
The odd thing is that I can always get it to heat up and stabilise, or cool down and stabilise. It's just that WHERE it stabilises seems to change the longer I have been driving.
The general effect is just like Pete suggested might happen if the sensor was reading dash temperature instead of air temperature.
In fact, before I found this forum, and where the sensor was located, I was convinced it lived under the seat - so that the longer I sat there the hotter it got[:I][:I]
Either there, or somewhere on the floor near to the exhaust.
PJ

Stempy · Post by **Stempy** » 08 Dec 2004, 23:15

Buy a can of freezer spray and keep it in the car. If it gets too cold just squirt a bit down the fan hole, the sensor will think it's suddenly gone down to -50 and put the heater on full chat.

RichG · Post by **RichG** » 09 Dec 2004, 00:51

Mine also does the same thing, or at least my wife is convinced that the car gets colder as the journey progresses.
I believe that it is all in the mind! When the cabin is cold the heater provides air that is hotter than the set temperature. Your body then gets used to this hot air so that when the set temperature is reached and no more heating is required your body thinks that it has gone cold. A bit like comming out of a sauna on a hot day. You will initially feel cold. If you fitted a thermometer in the cabin you would get an idea of the actual temperature.
My wife also complains of a constant cold draft from the fixed vents on the passenger side. Could be the 'wind chill factor'.Does anybody else get this problem?
Richard

petefa · Post by **petefa** » 09 Dec 2004, 02:38

Here is another idea!
My Xantia started to cool down on the passenger side, and also I had the same cooling down on a long journey.
The floor and the windscreen vents were also cooler than the middle vents.
Please not that this was a gradual process over many months.
The cause was a gradual blocking of the heater matrix, until I only had warm air from the middle vents and cool/cold air from the other vents.
If you have, from starting, warm air from all the vents, which then gets cooler, you might have air in the matrix.
Try undoing the bleed screw,(ONLY when the engine is cold and just started, the bleed screws are under pressure at normal running temperature and you will get burnt!!), where the heater matrix pipes go through the bulkhead.
If water comes out with no air bubbles, you have a gradual blocking.
See my other posts for a cheap but fiddly cure.
If you get water with air bubbles, then the system needs bleeding.
If you get no water out, then you have an airlock, then the system needs bleeding.

Panjandrum · Post by **Panjandrum** » 09 Dec 2004, 03:15

Thanks for the suggestions everyone.
This has been a bit of a mystery, and a cause of dispute between rational driver and subjective passenger, for years.
I will work my way through the suggestions as I get the chance.
PJ

CommY · Post by **CommY** » 09 Dec 2004, 21:15

When the slider is set all the way hot this overides the sensor and just gives 100% hot air so this means that the sensor or fan is not the problem.