Xsara Heater stuck on full blast!

This is the Forum for all your Citroen Technical Questions, Problems or Advice.

Moderator: RichardW

jaynay
Posts: 10
Joined: 12 Jan 2006, 12:32

Post by jaynay »

Thanks for all the posts - armed with this knowledge I had a look for the offending part in the passenger footwell.
I removed carpet and located what I think is the blower motor, but it isn't secured by 3 screws as mentioned - it looks like 1 screw and 1 bolt ?
Mine is an 02 registration - has the part changed ? or am I missing something ?

jaynay
Posts: 10
Joined: 12 Jan 2006, 12:32

Post by jaynay »

By the way, Caledonia Citroen (Newport) have quoted me £60 +VAT for an initial look see. According to them, worst case scenario is the whole heater matrix needing replacing which would cost around £600. Was interesting to find out what they'd charge I suppose...........!

User avatar
Clogzz
Posts: 2075
Joined: 15 May 2005, 18:04
x 18

Post by Clogzz »

The heater matrix has nothing to do with blower speeds.
So, beware of getting ripped off.
Simplest would be to try a blower from a wreck.
With a bit of luck, Xsara and Xantia blowers are the same.

jaynay
Posts: 10
Joined: 12 Jan 2006, 12:32

Post by jaynay »

I ordered replacement transistors from FarnellInOne (part no MJ15016G) at cost of £3.51 +vat each.

Removed motor from footwell (held in with 3 bolts rather than screws and wireloom is in the way a bit so it's a bit fiddly) and removed control board with pcb and transistors attached.

Drilled out rivets and de-soldered original transistors, and replaced with new ones. Put it all back together and......
no difference!

Blower still stuck on full blast.

Suspicion now falling towards dial controls in dashboard - any suggestions ?

User avatar
Clogzz
Posts: 2075
Joined: 15 May 2005, 18:04
x 18

Post by Clogzz »

Are the old transistors shorted ?
If not, the next hope is dry joints.
Any dodgy or corroded soldering ?
Try resoldering the control board.

jaynay
Posts: 10
Joined: 12 Jan 2006, 12:32

Post by jaynay »

The old transistors do not appear to be shorted.

No sign of corroded soldering.

If transistors were removed, would the fan work at all ? Or would that depend on the dial position on dashboard. If the dial is set to full, does it bypass the transistors ? Just trying to think of a way to eliminate or confirm the source of the problem. Wondering if dial is faulty and 'stuck' in full power state.

User avatar
Clogzz
Posts: 2075
Joined: 15 May 2005, 18:04
x 18

Post by Clogzz »

Does the car have 4 set fan speeds and an 'auto' position, because from what I gather, there are 2 sorts of air conditioning systems ?
The gathering comes from the French 'Planète Citroën' forum, where they say to use transistors MJ11015 only, and not anything else.
It also says that transistor-controlled fan motors are all the same for the ZX, Xsara, Xantia, 306 and 405.

If the transistors aren't in, the motor can't spin because all the current for the motor goes through the transistors.
On the transistor-controlled fan motor, the transistors are not bypassed on the full speed.
On the resistor-controlled fan, the resistor is bypassed at full speed, and then the fault is much more simple, caused by an open thermal fuse link, inside the shielded resistor, as here:

Image

To check for dial control fault, disconnect or short to earth the 2 thin wires at the motor, leaving only the thick red and black wires to supply and earth the motor.
If it spins like that, then the fault is in the transistorised controller on the motor.
I once saw a table of control voltages for the fan motor.
That place may have become a 'pay as you enter' forum, but I'll explore anyway, and post any finding worth sharing.

Best of luck !

jaynay
Posts: 10
Joined: 12 Jan 2006, 12:32

Post by jaynay »

The fan speeds are (in a clockwise order) Auto, 0, variable, Max. There are not 4 distinct speeds - 'Clicks' in Auto, then 0, then just an increasing scale then 'clcks' in Max position.

I got the MJ11016G transistors based on the list from Peter.N. in the linked topic you identified - but they are NPN polarity, whereas the MJ11015 is PNP, so have I got the wrong transistors ?

User avatar
Clogzz
Posts: 2075
Joined: 15 May 2005, 18:04
x 18

Post by Clogzz »

Yes, wrong transistors, they have to be PNP.
This is very strange, because usually it's one NPN and one PNP, complimentary transistors or whatever it's called.

jaynay
Posts: 10
Joined: 12 Jan 2006, 12:32

Post by jaynay »

Nobody's mentioned complementary pairs before ?! I'm well confused now.
And if Planete Citroen say only to use MJ11015, then that's only the PNP version for both, whereas previous thread had stated NPN.

I've just looked at the 2 old ones I took off they are both labelled the same (ST FW2G025A1) but I can't tell if they're PNP or NPN.

When I tested them, neither seem to be short circuit either, which is why I'm thinking it might be a fault elsewhere.

When I get the chance I'll try to test motor as you suggested with just red and black connected - might not be 'til weekend though.

User avatar
Clogzz
Posts: 2075
Joined: 15 May 2005, 18:04
x 18

Post by Clogzz »

Nothing to be confused about :D since there is no complementary pair here, as both transistors are the same.
The list of transistors may list complementary pairs, and that's probably how NPN's made it into the list, but we don't have them here.
The FW26025A1 transistors are the original PNP ones, that are unavailable, says planet.
This is where I got my story from, in French:

http://www.planete-citroen.com/forum/sh ... post480867

You need to log in to access:
User name (Identifiant): La brosse
Password (Mot de passe): 123456

If the transistors aren't shorted, it's not likely to be that, and the experiment with red and black wires may confirm that.

Best wishes.

jaynay
Posts: 10
Joined: 12 Jan 2006, 12:32

Post by jaynay »

Assuming everything else was ok - what would be the effect of having the NPN instead of the PNP transistors. Would it run at max or not at all ?

I'm going to have to swap them back again at some point, but do I need to do that before the red & black wire test ? (Will it affect the result?)

User avatar
Clogzz
Posts: 2075
Joined: 15 May 2005, 18:04
x 18

Post by Clogzz »

Impossible to say without seeing the diagram, that probably doesn't exist.
It normally wouldn't go at all because the current can't flow in that direction in an NPN transistor, and most of all the bias to the base will be the opposite to what's needed.
If the original transistors aren't shorted, then it's not that.
Without multimeter, it should be possible to test the originals with a small torch battery, lamp and piece of wire.
If the lamp lights between any terminals, in both directions, then the transistor is shorted.
I would try the old ones back in, if they show good after measuring, then see what happens with red and black wires only.
If the rotary speed controller operates as a potentiometer, then it may be flat-out all the time if it's open at the earthy end.


Addition 1.30PM GMT:

Just read on planet forum that the motor regulator is made up of 2 power transistors, a logics control board, and ... a bypass relay for the highest speed.
Never seen a relay on mine, it may be hidden inside the motor casing.
This does ring a bell, a story on 'froggy forum' about the 405 having a relay under the motor or something.
Froggy is off the net just now, which is most unusual, but I'll post the finding when they're back.

User avatar
Clogzz
Posts: 2075
Joined: 15 May 2005, 18:04
x 18

Post by Clogzz »

Talk of bypass relay, and other ideas here:

http://www.aussiefrogs.com/forum/showthread.php?t=32116

jaynay
Posts: 10
Joined: 12 Jan 2006, 12:32

Post by jaynay »

Well - we live and learn.....

I've just removed the blower motor again and the control board from that.
There is a relay underneath the pcb. (I'll post a picture of it when I get a bit more time.)

Out of curiosity, I removed the incorrect transistors and put the whole thing back together with no transistors at all.

Popped it back into the car and.....

The motor only goes when the switch is set to max, and stops at anyother position. This suggests that the switch is fine, and either the bypass relay was stuck and has now freed itself, or the transistors were at fault (either failed or something else shortcircuiting across ther terminals.

Then I put the original transistors back on and I'm back to full blast all the time. So it looks like it was the transistors after all. I'll now order some correct replacements (PNP) and do it all over again.