Author Topic: 12 volt electrical help needed please... (Read 4476 times)

Rotary-Motion · « **on:** January 06, 2013, 08:30:28 AM »

hi all

i got a problem with my car thsts very annoying, the car heater fan only works when it wants to. so sometimes i freeze and cant clear the screen or it works so i have to leave it on and cook myself...

so if i cant find the problem i was thinking of finding the fan wire and putting a rheostat or Potentiometer in the live wire and useing this to turn fan up and down, as im guessing the slide switch maybe the problem? im not sure.

a freiend said it has a regulater or some circuit board on the fan assembly that it could be? i've no idea.

any help appreiciated thanks guys...

Dickjotec · « **Reply #1 on:** January 06, 2013, 08:59:28 AM »

I suspect an ordinary pot would not handle the current. First thing is to wire the fan direct and see if it works, if you can get the slider out just by pass it and see if that solves the problem. It could be the brushes in the fan or a winding gone. Can you get to it? If so give it a thump and see if it starts.

Tony · « **Reply #2 on:** January 06, 2013, 09:54:16 AM »

A pot won't be powerful enough to handle a car fan.

They usually either have a ceramic resistor block in the fan flow to keep it cool, or an electronic circuit that drives the motor with a PWM signal (essentially very quickly chopping the 12V on and off to reduce the power).

Of course you can find the fan wires and directly put 12v on them for maximum power, but varying the power is a little harder (maybe get a resistor block and some switches from another vehicle)?

Tony · « **Reply #3 on:** January 06, 2013, 09:57:50 AM »

Or - this would do it.

http://www.ebay.co.uk/itm/10A-12V-40V-PWM-DC-Motor-Speed-Control-Switch-Pulse-Width-Modulation-Governor-UK-/261126997754

Amazing price for what it is

(Cheaper still from China or Hong Kong if you are prepared to wait)

Would be worth checking your fan is less than 10A but I can't imagine it's that powerful?

Edit: More powerful one from china with remote pot

http://www.ebay.co.uk/itm/12V-24V-36V-48V-30A-500W-DC-Motor-Speed-Control-PWM-Adjuster-Controller-New-/200818138029

greasemonkey · « **Reply #4 on:** January 06, 2013, 03:15:50 PM »

Is this a 406? There is a known problem with a circuit box. Eventually the fan will either be full on, or not working at all, with no controll over it. I belive the box that needs changing can be accessed by removing the cubby hole in the dash. A quick google should show you. its a common problem.

I don't know how much the fan pulls, but one I tried to fix melted a 30 amp relay in seconds.

That would really be the first place to have a look. Dont go near the switch, they are very delicate and there is nothing you can do to them, except maybe check for loose leads.

I'd bee looking at the circuit box.

Rotary-Motion · « **Reply #5 on:** January 06, 2013, 08:04:20 PM »

hi all

well i been investigating today and i have found out what it is, its a loose 2x terminals on the main motor armueture, but on the inside so i cant get at it, i tried hacksawing the casing off to see inside but its a sealed unit, also i think theres more going on than just bad contacting inside, so i decided i will go the second hand route.

just to let 406 owners know the fan is under the glovebox and easy to get to and it only had 3x screws holding it in, with 1x electrical connector. heres a few pic of the beast below.

i will say 1 thing the idea of dropping a switch in or rheostat in as mentioned above by GM is a no no, check out the size of the cables for this fan, there massive, i put some plumbers solder next to the wire for size, check it out in pic...

greasemonkey · « **Reply #6 on:** January 06, 2013, 08:38:34 PM »

IIRC the relay let out a scream before it melted. I then just taped the two wires to the dash board and twisted them together when I wanted the fan on. Then let out a scream myself when they either gave me an electric shock, or the spark burned me.
Looks like a simple fix anyhow.

Tony · « **Reply #7 on:** January 06, 2013, 09:15:36 PM »

Erm, yes, that is a mighty cable, looks rated rather more than 10A!

Head Womble · « **Reply #8 on:** January 06, 2013, 09:50:13 PM »

406 fans do draw a hell of a current, mine welded the ignition switch so I couldn't turn the key (yes they're switched at the ignition),
this was the day before we went on our holls,
ignition switch replaced and all was well.

A common mod is to run the fan from a 40A relay using the normall wires just to switch the relay,
this stops the ignition burning out.
The Xantia is the same.

1958steveflying · « **Reply #9 on:** January 07, 2013, 06:31:26 PM »

Quote from: greasemonkey on January 06, 2013, 08:38:34 PM

IIRC the relay let out a scream before it melted. I then just taped the two wires to the dash board and twisted them together when I wanted the fan on. Then let out a scream myself when they either gave me an electric shock, or the spark burned me.
Looks like a simple fix anyhow.

You did well to get an electric shock out of 12 Volt Dc.

greasemonkey · « **Reply #10 on:** January 07, 2013, 07:05:37 PM »

Quote from: 1958steveflying on January 07, 2013, 06:31:26 PM

Quote from: greasemonkey on January 06, 2013, 08:38:34 PM
IIRC the relay let out a scream before it melted. I then just taped the two wires to the dash board and twisted them together when I wanted the fan on. Then let out a scream myself when they either gave me an electric shock, or the spark burned me.
Looks like a simple fix anyhow.

You did well to get an electric shock out of 12 Volt Dc.

Often happens. Must have conductive hands or something. Especially if they are sweaty and damp.

Rotary-Motion · « **Reply #11 on:** January 07, 2013, 10:15:11 PM »

well i finally tracked down a fan shroud unit, i looked alot of 406's only to find the wrong ones there are 2 types, climate control (up down buttons) and non climate control (slide button), mine is non, tried pug vans and citreons to no avail.

as a last resort my mate spotted an old 405 model, which this has a 99% match so thats going in, fan same and same fittings re electrical and screws and housing, just looks slightly dofferent.

£25 notes...

anybody know what the 2x circle pots are on the heatsink please in below picture.

Head Womble · « **Reply #12 on:** January 07, 2013, 10:45:18 PM »

They're something to do with the fan speed, it's these that need replacing if it only runs at full speed.

If you need any more info try http://www.frenchcarforum.co.uk/ or http://www.406oc.co.uk/

greasemonkey · « **Reply #13 on:** January 07, 2013, 11:32:59 PM »

I'm not sure, but I think they are called transistors. They have a small voltage applied to them, that alters their conductivity, thus regulating the greater voltage/ amperage that controls the fan motor.
When they go kaput, they no longer increase their resistance as the control voltage rises, so the fan runs flat out.

I'm glad i deleted the post I put up about them being diodes now.

Bio Dervotee · « **Reply #14 on:** January 08, 2013, 04:05:32 AM »

Hi, they are transistors, heavy duty ones as used in output stages of power amps, they have 3 connections, emitter, base, collecter, a bit like a sink tap, emitter, water in/power in --collecter, water out/power out, --base is like the tap, turn it on more,more water/power flows. If the transistors fail then its usually in short circuit mode,ie full power to fan. fuses on these circuits are generally in 15--30 amp range, looks like they've done away with the big multi-tapped inline resisters and gone electronic. It also means that control voltages for fan speed can be done with low power/current rated wiring. That wiring in pic's is easily 30amp rated, so full power to the motor and light wiring to the control circuit.
cheers
hope this helps

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12 volt electrical help needed please...