Xantia Interior Heater Fan

[ecohouse1]

Sorry to ask this as I know it is a common query, but I searched and there seems to be a number of variations to this fault.

On my Series 2 TD estate, the interior heater fan operates only at the max setting - on max power, if I try & reduce to half power it just seems to go off. If I put it to Auto - sometimes it runs on max & other times it appears to be off!!

Is there a common culprit for this I can look at?

Many thanks in advance

Alan

[xmexclusive]

No intermediate fan speeds usually turns out to be the fan controller module darlington transistors faulty.

John

[Peter.N.]

Yep.

Peter

[xantia_v6]

No intermediate fan speeds usually turns out to be the fan controller module darlington transistors faulty.

John

But those transistors also switch the maximum speed, so if the fan speed control has any effect, then the transistors are OK.

Does the fan stop completely when set to auto, or is it just not moving enough air? If the latter, then the firsst thing to do is replace the pollen filter.

[xmexclusive]

I do not agree that you can give the transistors a clean bill of health from full speed fan running.
While the Darlington transistors can fail as totally dead they usually fail so that the fan still gives full speed or off.
I agree with checking the simple things first before replacing the transistors or the fan control module.

John

[Xaccers]

Are you certain it is going off? Quite often you can only hear them running when on full or nearly full speed.
Half setting for instance still blows air but you're not likley to hear the fan.

[CitroJim]

On my Series 2 TD estate, the interior heater fan operates only at the max setting - on max power, if I try & reduce to half power it just seems to go off. If I put it to Auto - sometimes it runs on max & other times it appears to be off!!

That could still be the transistors. Their normal failure mode, as xmexclusive says, is to go short-circuit which causes an uncontrollably fast fan at all settings. It will start running at top speed as soon as the ignition is switched on and stop only on ignition off. However, the full-speed setting is achieved by use of a relay on the regulator board so if, unusually, both transistors have gone open-circuit then full speed will still be available but with no intermediate speeds.

[ecohouse1]

Thanks Chaps

In fact I haven't changed the Pollen filter - I have one to go in but not had time. There might be what sounds like a light flow of air coming through the vents at intermediate settings.

I take it that the filter is behing the passenger footwell carpet? I remember in the Xsara it was behind the glovebox.

Thanks

Alan

[ecohouse1]

Yes on the subject of intensity - full blast in max - no problem - if I switch to Auto (what is this anyway?) it goes full blast although sometines low flow too.

[CitroJim]

if I switch to Auto (what is this anyway?) it goes full blast although sometines low flow too.

Auto mode puts the fan under the control of the climate ECU and it adjusts it's speed to help, in conjunction with the motorised heater flap, regulate the cabin temperature...

In auto, the fan will run fast if the cabin temperature sensor believes the cabin is too hot or cold as seen by the cabin air temperature sensor. Once the system reaches equilibrium it will slow down markedly.

If this is not happening then either your cabin temperature sensor is getting duff information or another sensor is seeing things wrongly.

The cabin temperature sensor is special as it hides behind the small grille in the dash trim above the wireless and has a small fan to blow cabin air over the actual sensor to ensure accurate readings. If the little fan stops then the cabin sensior wikll read the ambient temperature under the dash, which is pretty toasty generally, and use the blower in frantic attempts to cool down. The net result is the cabin temperature goes right down with a fast-running blower.