annoying whirring noise from roof console, What is it ?

[blue94auto]

Hello all ,I have been bugged by this annoying noise on my s2 2.1 hatch,when the ignition is on and engine is stopped it is most notable.
I removed the roof console and found the culprit,it is a cylinder shaped thing with wires going in one end and a small fan on the other.
I have disconnected it and the car seems no different.
Can anyone enlighten me as to the function of this thing.
I thank you in anticipation.
Gary

[noz]

Hi gary,

The little blue thing in the centre is a thermistor, a resistor whose resistance changes with temperature. This is the temperature sensor which is used by the heating system to control the cabin temperature. The 'cylinder' is actually a little fan. Its purpose is to draw a sample of the cabin air across the sensor to read the cabin temperature. Without the fan the process of sensing the changes in cabin temperature is simply slower. In some cases it can be so slow that the temperature swings wildly from one extreme to another.

I have the same problem. When the temperature outside is 5DegC and below the fan makes a terrible whining noise until the air heats up. Once the heater is working and the air temperature rises the noise stops. It does not happen through the summer months. I suspect it is the fan impeller striking the side of the cage due to worn fan bearings. I've tried WD40 with no success. I'll ned to further investigate the problem.

Removing the sensor will simply result in the heater not working. The controller will think the temperature is permanently high so the heating will be permanently switched off (matrix bypassed).

Hope that helps your understanding.

Cheers

noz

[kenhall1202]

I sorted out my shrieking roof console fan by cleaning out all the accumulated gunge (use cotton buds) and then applied 3in 1 oil - quiet ever since.

Ken

This post has been edited by kenhall1202 on October 01, 2010 04:51 pm

[blue94auto]

Thanks for the quick response chaps and clearing up the mystery.It is such a relief to pull up at the lights and not hear a clicking under the glove box or that damn thermistor fan whirring away.
would you believe it,apart from the thermistor making it's racket,there has been a clicking intermittently from under the glove box,I took the glove box out earlier on today and we have just covered about 15 miles with the Friday shopping expedition and there ain't been one click,the silence is lovely.
I noticed there is some gunge around the fan blades I will try cleaning it as you suggest and give it some light oil.
I will keep you posted.
Thanks again,Gary

[xmexclusive]

Hi blue

The clicking under the glove box is usually caused by the indicator switch.
The switch can suffer contact wear internally and the smear of grease present can get partially conductive. The switch can then suffer high resistance tracking between contacts. Just enough voltage leaks through to click the relay.
Try giving the switch a little nudge next time there is clicking as that can sometimes stop it. Replace switch or take to bits to either clean off grease or repair.
All have been covered on the XM sites.

John

This post has been edited by xmexclusive on October 02, 2010 09:03 am

[blue94auto]

Thanks for that John It has gone silent now, yesterday I was driving the car with the glove box removed and there was no clicking,last night I had repaired the handle on the glove box and fitted it back in,took it for a good test drive still no clicking,if it happens again I will do as you say.
Noz I have that thermistor fan out of the car as I have not yet cleaned it,on driving the car yesterday the heater is still working quite good . When I say quite good I mean heat wise,the blower will only work on the fan position,I have ordered two MJ11015 Darlington transistors and look forward to hopefully getting all the fan speeds working soon.I have read your fan fix pdf in the self help section,very good noz.
The silence is golden,
Gary

[blue94auto]

Just like to say thanks Noz I fitted the two MJ11015 transistors as per your self help file,now I have all fan speeds working. Nice one.
Gary
ps I couldn't find my rivet gun so I used some small machine screws and dabbed the thread with loctite, they ain't going anywhere.

[messerschmitt owner]

ah

that explains my non working heater in the green car!

Thanks