Xantia Blower Fan Speed Control: Testing

[CitroJim]

Clogzz, I apologise for invading what is very much your territory here. I hope you will not mind if I add the following to the blower fan issue.

Lately, I've been sent two blower speed regulators for repair as the fan was spinning at top speed uncontrollably. On test, both these modules were found to be perfect.

This little post is a brief guide to some more tests that can be done when the module itself is known to be OK.

Firstly, here is the wiring diagram of the Climate Control on a Xantia. It's a MK2 but the MK1 is very similar.

With reference to the diagram, Item 8045 is the blower speed regulator and Item 8080 is the Climate ECU. Item 8025 is the heater control panel which includes the fan speed slider. It's not a switch, it's a pot.

Looking at Item 8045, Pin 3 (wire 16, orange) is the speed control input from the ECU. There will be a voltage here and this varies with fan speed.

Typical voltages are as follows:

Note the engine must be running. Outside temp about 18 degrees, car parked in full sun. Measured on a MK1 2.1TD.

Slider set to off: 12V (actually full battery voltage)
Slider at speed 1: 9.8V
Slider at speed 2: 8.4V
Slider at speed 3: 5.6V
Slider at full speed: 0.9V (almost earth)
Slider on Auto: 7.5V approx.

As can be seen , an earth on this wire will give full speed whereas full battery voltage will stop it.

If the module is OK, a flat-out uncontrollable fan that runs all the time irrespective of engine running or not (the fan only runs after the engine is confirmed to be running by the Climate ECU) can only be the result of the orange wire finding a false earth somewhere, either because of wiring damage, a short in the connector (it is next to the big black earth wire in the plug) or a duff climate ECU.

If the fan runs flat out only when the engine is running, this may indicate a faulty slider, a duff ECU again or a duff temeperature sensor. Items 8034, 8006, 8037 and 8032 are various sensors dotted around the heater box and if one is duff or has a wiring fault, that could give rise to the fan running continually fast to try to resolve the temperature issue the duff sensor is seeing. The simplest way to check the sensors is with a Lexia diagnostic check on the Climate ECU.

The fan regulator itself has a temperature sensor on the heatsink and this comes out on Pin 1 of the plug (wire 17, white). The function of this is to regulate the speed against changing transistor characteristics with themperature and to guard against possible thermal runaway in the output transistors if they get too hot. If you measure on this wire, you will typically see around 0.45V.

[DickieG]

Nice one Jim, Clogzz will find the linked diagram easier to read than "us lot" in the Northern Hemisphere .

[Clogzz]

Hello Jim and Richard,

No risk of offence, it’s all very welcome, and I’m sitting here with my feet up; watching all that go by itself.
And thanks especially for posting the map to our down-up benefit.

[CitroJim]

And thanks especially for posting the map to our down-up benefit.

I must post up a Northern Hemisphere version of that diagram Clogzz!

For those looking at this diagram in the Northern Hemisphere, please rotate your monitor through 180 degrees.

The diagram will also print upside-down but if you similarly rotate the paper through the same 180 degrees, it'll appear to be the right way up

[handyman]

Jim, there is an alternative in viewing the antipodean wiring diagram, but it does require a certain level of advanced fitness. Head or handstands! 8)

I have noticed a recent influx of new members coming in from the cold, many echoing the same problems us old lags have resolved. Maybe it is time to add another sticky listing likely electrical/electronic issues as these cars are now getting even older! Maybe a sticky cross linking the issues with threads from the archive, as none of it is exploring new territory?

Handyman

[Clogzz]

rotate the paper

Jim ! That’s a sensational discovery !
No wonder that civilisation originated in the Northern Hemisphere.

Windows picture and fax viewer allows rotation of images, but warns of reduced quality of large pictures.
I rotated and saved this very large picture without any loss of quality.

[hamster99]

Oh dear.........i've read all the info you guys have about the blower and aircon system on the Xantia and am still stuck as to what my next step is. I thought it was the ignition switch as that seems to be a common theme but that all checked out OK. My system just stopped working full stop one day, no warning or anything.

Now it seems like I have hit a brick wall as I have the climate control system and nothing works (except the aircon switch light..!!). As I am not good with meters and voltages etc what's my next move.........it seems so complicated do I have to resort to a very expensive visit to a dealer???

Cheers

Robert

[MikeT]

Hello Robert, what's has stopped working, the blower fan or your A/C or both?

Regarding the blower fan, have you checked the obvious first - fuses?
If they're ok, check the power connectors to the blower haven't been knocked out of place as they live just above the passenger footwell and I suspect are susceptible to knocks.

[hamster99]

Hello Robert, what's has stopped working, the blower fan or your A/C or both?

Nothing works, blower or AC

Regarding the blower fan, have you checked the obvious first - fuses?

Fuses are all OK

If they're ok, check the power connectors to the blower haven't been knocked out of place as they live just above the passenger footwell and I suspect are susceptible to knocks.

I took out the blower fan and connectors were fine. Checked the terminals for signs of power but nothing.

[Xaccers]

I took out the blower fan and connectors were fine. Checked the terminals for signs of power but nothing.

If the engine is running and you're getting no power to the two thick contacts in the brown fan connector block with your multimeter set to something like 20v DC then I'd say your ignition switch has burnt out too much.
Get the panel off the steering column and check for continuity from the switch connector to the brown fan connector, and also from the fan connector block to earth just incase there's a break in the feed.

[allanmc]

Jim, thanks for the e-mail about the blower I am beginning to think that this is too technical for me, anyway I pulled the plug on the motor and took a reading between the black and the red wire with the engine stopped and it was 12.18 volts with the engine running it was 14.0 volts I then took a reading between the black and orange engine running it was 1.3 volts I am afraid that this means nothing to me, so is there a way of making it easier for me. Thanks
Allan

[MikeT]

You're doing good Allan, just wait for Jim (or other blower experts) to assess your findings and it'll all come clear in the end. One thing that does cause confusion, as said above, is that the blower will not work unless the engine has been started, by design.

[addo]

I'm still rooting about with this on my estate.

Duff setup; fan control set wherever and still it will put out charge voltage at times (approx 14.3V) then flick back to "normal". Auto or manual makes no difference.

Stuff that I wonder about:

1. The control slider pot (by thresholds) controls the ECU driver IC - using a linear op-amp - correct?
2. Can a fault condition with the Bitron cooling circuit cause the climate ECU to stop the fan? I ask because a well-worn high resistance fan relay in an XM/605 will mean the fans don't both work reliably, and I can imagine a "failsafe" condition shutting off potential further engine load (via climate control) if it can't guarantee adequate cooling. Haven't tested by popping off the Bitron sender switch but suppose this is an option!

I'm leaning towards a dying op-amp or dry joints in the climate ECU.

[addo]

I've played around some more and made the discovery that briskly flicking the temperature slider across, often restarts the cabin fan. That probably rules out relay issues - I had earlier tested both relays and they showed normal resistivity. Still reckon the climate ECU is a likely cause.

[Clogzz]

There’s nothing to reduce the load, except for the compressor in case of overpressure.
The Bitron doesn’t know about the interior fan, nothing works upstream in the Xantia.
With a bit of luck, the cog under the speed slider is falling out.

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