Xantia Fanproblem

[sarvjohan]

Hey!

So I've browsed around here and found many with a similar problem with the fan stop working. And since i'm quite the beginner with cars in general I did an attempt and failed.

It started with my fan all of the sudden started to blow at max speed at all times. Read alot about the problem and stuff around it. Decided to go with the solution to change transistors. So I ordered a new pair of transistors MJ11015G if i'm not wrong. And everything ran smooth, removing fan and after some struggle changing the transistors aswell.

Problem I have now is that when I start the car with the fan off. And I turn it on it runs for like 2sec then it dies. This is everytime I start the car. Thought it might be a fuse the first time but then it should only have worked a few seconds the first time and not after. That is if there is no automatic fuses which I assume there isn't.

Anyone have any tip? I'm lost

It's a -99 model.

[CitroJim]

Welcome to the forum

My guess here is that you've displaced/lost the little disc thermistor that sits on the heatsink in a circular well. This thermistor guards against thermal runaway if the heatsink gets too hot and will then gracefully close down the speed regulator to protect the transistors.

The thermistor disc contacts the printed circuit board via a small spring finger...

Check it's still in place and making contact with its contact finger...

It's easy to loose it when busy replacing the transistors. You used the right ones but did you ensure they came from the same batch? If they come from different batches one can run very much hotter than the other and could trip the over-temperature protection discussed above.

The batch number is the 'other' letters and numbers on the top of the transistor..

[sarvjohan]

Ahh, yeah I had some troubles with that thermistor. Gonna check it tomorrow to see if it's there, or maybe it lacks contact since I didn't have any copperpaste to add to it.

I'll check the batch aswell tomorrow and return with some new questions

Thanks!

[CitroJim]

I'll check the batch aswell tomorrow and return with some new questions

Thanks!

No worries, ask away

[sarvjohan]

So it seems to be the same batch, and the thermistor is still there. Bought some copperpaste to add so it gets better contact.

Was thinking, when i removed the old transistors they had this sticky white stuff on. I'm gonna assume it is to not get contact against the metal? And I never added anything new there. Do I need to add this aswell or should that not be a problem?

Since I got the fan inside and broken down in pieces might aswell fix everything once I'm at it :p

[Old-Guy]

...when i removed the old transistors they had this sticky white stuff on.

This is what's usually known as heat-sink paste (thermal conductive grease/paste). It's essential purpose is to conduct heat from the transistors to the heat-sink (and from the heat-sink to the thermistor). When fresh, it's the consistency of toothpaste. With age it dries out but generally continues to do it's job until disturbed.

Without the good thermal path to the heat-sink, the transistors will fry themselves and the thermistor won't be able to get a sensible temperature from the heat-sink.

You should be able to get a little tube of it from any shop that sells computer spares or online from someone like Maplin.

[Hell Razor5543]

Personally I would use silver conductive paste (if you can). It is somewhat better at conducting heat, and it doesn't go hard (which may be a point against it here, as it may be being used as a glue as well), so if you have to take the heat sink off in the future it won't put up a fight. This is the sort of stuff I mean;

http://www.ebay.co.uk/itm/Arctic-Silver ... 2a52d22d4a" onclick="window.open(this.href);return false;

[sarvjohan]

Ahh okey, so it's to connect not keep away.

Bought a tube at the computerstore on my way home so I already have one that I bought for the thermistor. I'll remove the transistors and add it there aswell then!

But that itself shouldn't cause the fan to stop after two seconds?

I'll start over and add the paste to everything and try the fan again.

[CitroJim]

Lack of heatsink compound could as the transistors may have their own protection built-in..

never use too much paste. A light smear is all that's needed and no need for any of the fancy stuff.

Make sure the transistors are tightly bolted down to the heatsink. Don't solder the base and emitter wires until they are fully bolted down.

[sarvjohan]

A thought just struck me, do I have to worry about any polarity on the transistors? Cause I have no clue how the old one were mounted. -_-

[Hell Razor5543]

OK, so the fancy stuff isn't needed. I am just used to using it in PCs, where heat issues can cause weird problems (so I always use good quality silver paste).

[sarvjohan]

Late answer due to personal stuff that made me put the fan aside for a while!

Pulled it apart and added thermal compound to everything and put it back together. Runs perfect!

Thanks alot people!

[CitroJim]

That is excellent Delighted to hear it!