BX heater fan max speed relay - WHERE ?

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jack.dempsey
Posts: 116
Joined: 05 Mar 2003, 18:57

BX heater fan max speed relay - WHERE ?

Post by jack.dempsey »

I've removed various bits of my dash trying to locate this little tinker. The Haynes book of fairy tails says its located on the right hand side of the steering bracket - then on a relay location diagram show it somewhat left of centre just to the right of the fuse box. My blowers gone AWOL although spins when 12 volts are applied directly. I changed the speed control unit on spec - although I thought it might not be this 'cos when this failed on another BX a long time ago the fan would either run at full chat or not at all (the relay does this I think). I'd like to locate it now as its become a personal vendetta and I'd like to (as the police would say) remove it from my enquiries. Anyone know where ti is ?
Jon

Post by Jon »

Unless I'm being dumb (quite often) is it not all controlled by the resistor that secures to the side of the heater blower unit with 2 screws? I was not aware that the BX had a max speed relay for the blower, certainly if the fan works with a direct 12v feed then usually the fan resistor is the usual suspect. Helpfully it can absorb water and corrode due to its location in the scuttle area under the bonnet!!!
jack.dempsey
Posts: 116
Joined: 05 Mar 2003, 18:57

Post by jack.dempsey »

Indeed, and as I said, that was my first port of call (easiest first that's my motto). Unless I've fitted a 'duff' unit, changing that did not do the trick and my fan remains resolutely stationary. The control unit is basically a 'power' transistor that takes the relatively low current from the fan speed knob (on the dash) and controls the high current thats needed to spin the heater fan. I'll keep searching - I think I've seen a little box (on the steering bracket) that may be the relay - the colour of the wires that go to it don't agree with the Haynes diagrams so I'm not holding my breath. Oh to have at least four very flexible, rather long, slender arms to get in behind the steering column in a way that allows me to actually do something (like hold a spanner or turn a screwdriver).
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AndersDK
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Post by AndersDK »

Jack -
This max speed relay is located either on side of the steering coloumn/bracket - or behind (upper) glovebox as part of the wiring loom.
It's recognised by it's 3 heavy gauge YELLOW power wires - and 2 thin gauge green wires for control.
One of the yellow wires will have a brown 10mm marker - indicating this is the earth wire (as the blower is controlled on it's LO side).
One of the small green wires have a brown 10mm marker - indicating this is the +12V feed to the relay coil.
One of the 2 remaining yellow wires will be eactly the same yellow wire as found single in the blower department - where you have a 2pole connector in front of the blower housing.
On this 2pole connector you have a second yellow wire fitted together with a smaller green wire - which is the +12V feed to the max speed relay coil.
Check exactly this small green wire out here where it's exposed to weather conditions - chances are it's rotten away.
The whole circuit is feeded off fuse F2 (no 2 from left in fuse/junction box).
jack.dempsey
Posts: 116
Joined: 05 Mar 2003, 18:57

Post by jack.dempsey »

I know I've got 12 volts at the fan (from F2), its the earthy side, via the speed control/electronics and relay that isn't 'playing' (in fact I measure 12 volts on that side also but that makes sense if there's nowhere for the volts to go). Thanks for the info - I'll try and wind my head in behind the dash, when I get home tonight, and have a more meaningful look. Question is have I fitted another dodgy controller or is it something else - anyone want to start the betting ?
tomsheppard
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Joined: 19 Dec 2002, 15:46

Post by tomsheppard »

I'd check the slider on the speed control pot if I were you, Jack. This tends to work loose and contact is no longer made. An easy check IIRC is to pull off the speed control knob and push down the plastic ring below it which carries the wiper while at the same tiime pulling on the shaft that lies inside the control knob. This forces all the bits back together. the transistor (think of it as being a tap for the voltage) is bypassed when at full speed so if there is a duff transistor, there should be full speed available so if you have no luck, turn the shaft fully clockwise and try again. No fan= failed supply to PCB or a crack in it.
jack.dempsey
Posts: 116
Joined: 05 Mar 2003, 18:57

Post by jack.dempsey »

Just what I thought - the fan should run at full speed with the control fully clockwise even if the speed control electronics is duff. That is why I was looking for the relay. I'll try your excellent suggestion of pushing and pulling to get rid of 'play' from all the various bits and see if this results in any activity at the fan. Can't wait to get home and be surrounded by French engineering.
DLM
Posts: 524
Joined: 13 Aug 2001, 03:01

Post by DLM »

I'll vouch for the effects of a push and pull (on the speed control knob) - that's exactly what mine needs to work consistently at the moment.....
jack.dempsey
Posts: 116
Joined: 05 Mar 2003, 18:57

Post by jack.dempsey »

Hmmm...it seems my problem does reside within the dash control - on examining the circuit board that comprises the heater 'control' the 'printed on' variable resistor 'stuff' is cracked and burned at one end. If I short out pins 3 and 4 on the boards connection block my max speed relay engages and the fan spins full chat like it should. Looks like I need a replacement circuit board as this seems to be 'cream crackered' and beyond repair. I seem to have lots of bits of dashboard spread in both foot wells - hope I can remeber where all the bits go ! Anyone got one of these going spare ? I shudder to think how much main dealer will want for this little PCB - or if they can even get them.
oilyspanner
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Joined: 26 Oct 2003, 17:08

Post by oilyspanner »

I have a spare heater card in my bits dept
Stewart
jack.dempsey
Posts: 116
Joined: 05 Mar 2003, 18:57

Post by jack.dempsey »

How much..? (I've emailed you directly on this subject)
tomsheppard
Posts: 1801
Joined: 19 Dec 2002, 15:46

Post by tomsheppard »

If it is cracked, solder a 680 ohm resistor across it. Now here's a funny thing! My last BX didn't engage the relay and nor did the new one.
I don't believe that they ever do because-
I have identified a fault in the pcb manufacture.
Below the printed resistor, there are two tracks with a gap between them 2mm wide. If you were to solder the two tracks together with a link, you would have two enclosed brown areas on the pcb
divided by a thin track running vertically to the left and below the printed resistor. Cut this thin track as well and you now have the correct circuit as per the Cit wiring diagram. And the Blower relay comes in. I did this today. DLM was sceptical but he has seen it for himself.
tomsheppard
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Joined: 19 Dec 2002, 15:46

Post by tomsheppard »

I have just placed a rather blurred picture on my website tomshep.co.uk for your contemplation under bx heater panel
DLM
Posts: 524
Joined: 13 Aug 2001, 03:01

Post by DLM »

It worked - I was that witness!
1Dude
Posts: 4
Joined: 05 Mar 2004, 00:26

Post by 1Dude »

Now this is getting interesting. I have NEVER had a BX where the full blower speed relay comes on without a modification. As Tom has discovered and my previous investigations have shown that all the PCBs have been reworked by Citroën or their suppliers to remove the full speed connection to pin 4 by drilling a hole through the track !
As the result of this is that there would be zero output at maximun rotation of the blower speed dial a secondary link was introduced on the PCB back up to the usually used path to pin 4 for blower operation at less than full speed through the printed resistor of around 0.5k. This was in the form of a soldered link on the rear of the rear of the PCB on the early BXs and a permanent circuit on the board on later models- around 1990.
The reason for this defies logic. The high speed relay is still fitted to all models - so it is not a cost saving move - but full speed can never be used due to the PCB rework.
WHY ???
Any ideas.