Xantia heater either cold or very hot

[eye_flys]

My Xantia has an annoying problem with the heater, it's either a furnace at 30 degrees or blowing cold a couple of notches down with no in between. Is there an easy fix or do I need to attack the dashboard with torx bits?

[CitroJim]

Yes, maybe you'll need to crack out the old Torx bits...

Common reason for this bizarre behaviour is failure of the cabin air sensor. This lives behind the little grille at the LH end of the dash next to the clock. S1 Xantias have the alarm LED in the middle of the grille.

Anyway, the sensor is a bit clever and has a little fan behind it to draw air in from the cabin and flow it over the sensor element to get an accurate reading. Normally the fan gets clogged with dust and rubbish and a good blast of air down it may free it off but not always.

You can see if the fan is spinning by shining a torch down the grille and watching. It's hard to see but easier to see it not running and then switching on the ignition and seeing it move and spin.

If the fan is stopped then the sensor effectively reads the under-dash and wireless temperature which is hot and thus the heater will try to cool it down.

[Peter.N.]

I had a similar problem with my C5 for a different reason, that was due to the outside temperature sensor showing it was about 60C all the time, the system kept on shutting the heat off and putting the aircon on.

The XM had similar problems to the Xantia.

Peter

[Mandrake]

If its blowing hot air on the maximum setting but cold a couple of notches down I don't think it will be the cabin sensor fan (if the problem is there right from cold) - that would tend to make the sensor read too cold due to thermal time lag (assuming warming the car up from cold) whereas the symptoms suggest that the sensor is indicating the cabin is too hot. More likely the sensor itself is faulty.

If there are any forum members near you with a Lexia you can read all the temperature sensor readings with the Lexia and you should be able to immediately identify the fault. My guess is the cabin temperature sensor is open circuit giving a false hot reading for the cabin.

The maximum setting for the temperature slider just sets the heater flap to fully hot regardless of the measured cabin temperature. (No automatic temperature regulation at this setting - its a manual override) As soon as you go down a notch or two it goes back into automatic temperature regulation mode.

[exect]

Hi,
My fan has packed up but Jim did not say how you get to it, is it through the radio opening?
Exect

[Mandrake]

I haven't had one out but I suspect through the radio mounting hole would be the best way to gain access.

[CitroJim]

Half and half. You need to go in through the wireless opening to disconnect the wiring connectors to the sensor but to remove the sensor itself you need to remove the switch/clock panel which mean removing the wireless anyway..

It differs a bit between S1 and S2 but generally the above is the case...

[Hell Razor5543]

It might (only might) be worth giving the sensor grille a shot of compressed air from a can of air duster (these are lowish pressure, so shouldn't cause damage that a high pressure airline might). If the fan has become clogged with dust that could stop it turning, and a short blast of air could shift the dust.

If you want to see an example, just look inside your PC and see how much dust there is in the fans.

[CitroJim]

If you want to see an example, just look inside your PC and see how much dust there is in the fans.

I know Scary isn't it...

[Old-Guy]

If anyone is taking out a cabin sensor fan, could they photograph and measure it please?

I have a box of 12V fans taken out of scrapped PCs - it would be handy to know if any of these might be cannibalised to repair sensor fans. Frame design/dimensions don't matter too much, I've successfully transplanted a CPU fan/motor into an expensive graphics card which had a burnt-out fan.

[Mandrake]

If anyone is taking out a cabin sensor fan, could they photograph and measure it please?

I have a box of 12V fans taken out of scrapped PCs - it would be handy to know if any of these might be cannibalised to repair sensor fans. Frame design/dimensions don't matter too much, I've successfully transplanted a CPU fan/motor into an expensive graphics card which had a burnt-out fan.

I think you'll find dimensions do matter... the one behind the dash is tiny - its only about 10mm, maybe 15mm in diameter at the most, you won't find many if any fans that size in a PC...

[RichardW]

It's a rather odd thing, being an axial flow fan - and it's driven by a DC induction motor - the electronics fail and the fan just refuses to rotate. Had a failed one on my second Xant, then replaced it with a used one which also went west. It then hung out of dash board for about 2 years, worked fine there without the fan! Current one has run to 140k / 12 years, and is still working OK. They're quite dear from Citroen.... not as bad as I thought - there was a change on later cars, early S2 ones are £50, later ones £40, S1 ones £48