The definitive heater modification

Frequently asked technical questions and common modifications/improvements
Doz
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The definitive heater modification

Post by Doz »

Ladies and Gentlemen ...

The heater control modification. Enables the fan to run at full speed using the relay already fitted above the steering column.

Image

Whilst you have it apart, clean the track behind the control with a cotton bud moistened with alcohol and the contact strip on the knob itself. Also worth checking/ changing the bulbs.

And there you have it ... warm feet AND a defrosted screen at the same time \:D/

Reassemble, ajourn and celebrate your hard work with a beer...
Doz

2007 Citroen C1 (it's not a real Citroen)(With a complete set of wheel trims)
2006 C4 1.6VTR+ (Alloys no wheel trims)
1982 Mini HL (No wheel trims, no wheels)
1993 Kawasaki GPZ500
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tom
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Post by tom »

We did. Thanks for the picture. It will make life a lot easier.
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Mr B
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Post by Mr B »

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Kitch
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Post by Kitch »

This could be done from the front could it not? Without pulling the whole panel out and trying to unhook all the cables etc?
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Doz
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Post by Doz »

Kitch wrote:This could be done from the front could it not? Without pulling the whole panel out and trying to unhook all the cables etc?
Can't see why not
Doz

2007 Citroen C1 (it's not a real Citroen)(With a complete set of wheel trims)
2006 C4 1.6VTR+ (Alloys no wheel trims)
1982 Mini HL (No wheel trims, no wheels)
1993 Kawasaki GPZ500
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Kitch
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Post by Kitch »

So cut a section out of the strip and solder between the other two?
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jeremy
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Post by jeremy »

You don't need to unhook the bowden cables. The circuit board etc comes out quite easily.
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tom
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My Cars: 2003- Passe-Partout 1.9 TGD estate
2005 Grolliffe Tizzydee turbo estate and sundry other BXs and Grace, a CX TRD.
2008 to 2023 - all sorts of stuff, some interesting
2024. TxD 1.9D estate. 'Wheelybin'. Much worse than expected. Scrapped.
2025 Grogan. 1.9 TD Evasion Image Break. LHD.
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Post by tom »

You don't need to. it can be done in situ without removing the board. Just solder a wire across the track. 15A fuse wire will be fine.
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simonineaston
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Post by simonineaston »

Why do I modify the pcb you refer to - and how!?
I'm glad I asked! I'll be a bit disappointed if I find I don't have this type of PCB when I get the panel off this week-end...
This forum thing is dead good - can't beat having your own team of mechanics on tap, just waiting to offer helpful advice :-) Cheers, Chaps - I just hope I can get to be as helpful one day when I've learnt more about BXs. My previous 2 cars were Japanese sports cars - MX5 and MR2 - and lovely tho' they were, they were also a bit boring in that I never had to anything to either of them (except replace the clutch slave cylinder on the MR2 - useful training for the BX cam belt change as it requires small hands and double-jointed wrists and elbows... )
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Doz
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Post by Doz »

A step by step guide....

1) Pull off control knobs, and undo two philips/torx screws behind temparature and feet/face/screen knob. Turn air control knob on centre console vents to off (prevents springs from disappearing into the air duct) GENTLY remove vents, catch little springs.

Image

2)Locate metal retaining tags just behind the vent holes to left and right, and hook a flat screwdriver behind the tag and prise it outwards to release the front panel.

Image

3) Cut the track carefully using a pocket knife or similar (ask an adult to help at this stage!) and solder some wire across the other track.

Image

Your circuit should now look like this:

Image

Switch the ignition on , wind the wind :lol: control to max, you should hear the relay behind the steering column click, and the fan speed pick up. Check the bulbs , and reassemble!

Image

Cool .... 8)
Doz

2007 Citroen C1 (it's not a real Citroen)(With a complete set of wheel trims)
2006 C4 1.6VTR+ (Alloys no wheel trims)
1982 Mini HL (No wheel trims, no wheels)
1993 Kawasaki GPZ500
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paulwitchard
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Post by paulwitchard »

I think I'll have to find the soldering kit - and fix the bulbs - I wasn't going to bother but this seems to make removing the switches worthwhile!
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Philip Chidlow
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Post by Philip Chidlow »

I'm inspired. So am I right, the fans won't operate at full chat without this modification? And I assume in which case it does no harm the the blower motor over time.
• 1992 Citroen BX TZD Turbo Hurricane
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jeremy
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Post by jeremy »

The speed control on BX heater fans is achieved by the use of transistors which do a very good job but always have a residual resistance. The system is designed to remove this residual resistance by simply bypassing the transistors to enable full power to be delivered to the motor - and they did it rather nicely using a relay rather than a big switch on the dashboard. The only shame is that someone got the circuitboard wrong!

As for motor life - its designed to work in this way. Its not compulsory to run the thing flat out all the time - and you would probably get too hot anyway! Full speed is only achieved when the knob is rotated fully clockwise, the variable slower speeds remain undisturbed.
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kiwi
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Post by kiwi »

I feel a modification about to take place :)
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