12 Volt switch problem

This refers to a car switch but is not really a car specific problem.
My car heater switch has 4 power positions, if the aircon is switched on it starts when the heater switch is turned to position 1 through to 4.
Now for some reason my heater is not working on position one although the aircon kicks in, the heater works fine on positions 2 through to 4.
This has thrown me, if nothing worked on position 1 then I could understand it but if anyone can give me an idea I'd appreciate it.
Geoff Lane
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wrote:

There will be a resistor pack to regulate blower speed. The first resistor is dis. If you let us know what car it is, someone will be able to tell you where it's mounted.
Andy C
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These resistors run hot, so they're almost always mounted in the fan's own airflow, usually right next to it.
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wrote:

If it's a Ford, its right above the passenger footwell, fixed with a single screw. Very common problem. Often caused by the pollen filter being blocked and in need of renewal, restricting the airflow in the system, and not properly cooling the resistor pack, which is, as Andy said, mounted directly in that airflow.
Arfa
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For reference - a Ford Focus (circa 2001) blower motor circuit and position of the resistor pack can be found at http://www.amac.f2s.com/Focus1 /
If (and it's a big if) the original poster's car has the same or a similar circuit then a failure of one of the speed control resistors would cause a permanent failure, even when the A/C was turned on.
Still assuming a similar circuit, the explanation would be the switch has mechanically failed in that position. In the circuit shown in the above link, the slowest blower motor position is also connected to the heater control module and if by turning on the AC that connection (labelled Cb) is switched to 0V then the blower motor will again work in the slowest position. i.e. there are two methods of switching the bower motor on in it's slowest setting and the AC probably overrides the switch.
The AC probably does override the switch in order to turn on the blower motor when the switch is in the off position.
If its a Spanish built Vauxhall then the connector has probably fallen off the back of the switch, or is just about to :)
--
Alan
news2006 amac f2s com
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Sorry for delay in replying.
Car is a Nissan Micra.
Geoff Lane
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Resistor pack. Been there, done that.
Make of car?
Al.
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On some Nissan cars the resistor card has two contacts that are bridged with solder acting as a thermal fuse and these are a common source of failure on these cards. Repair is to clean of the contacts and resolder. Trevor Smith
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Thanks for all the suggestions folks, the resistor is easy to get at right by the heater blower motor.
New replacement about 30 so not too expensive, could try a breakers but honestly how much can I save and is it worth the aggro.
Geoff Lane
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I have a similar problem on a Mazda 626. The resistor pack has failed for the second time. A new pack here in NZ costs the equivalent of UK 50 pounds. Why are they so expensive, and why can't I just cobble up a new pack from some huge resistors that I have lying around?
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wrote:

Why indeed ... ?
Arfa
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You can. Bear in mind that the resistor pack runs so hot on some makes (Audi and BMW spring to mind) that the solder will melt! ISTR that when I fixed my BMW pack I just had to re-crimp the connections.
It seems terribly inefficient to me to have red hot resistors when there are better ways to control fan speed. But it's the cheapest option for the manufacturer :(
Al.
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Al wrote:

Actually, these days it probably isn't. But inertia and total lack of comprehension about electronics by auto designers is a key issue.
As an electric toy plane flyer, I can get an infinitely variable PWM controller for about 50A for under 30 quid, retail. Couple that to a 5 quid 'servo tester' and you can have infinitely variable and very cool running fan control for less than the cost of the spare resistor pack....
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What BMW do you have? Most for the last ten years or more don't use a resistor pack - it's an infinitely variable speed controller. Which is even less reliable than resistors...

--
*Learn from your parents' mistakes - use birth control

Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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It was an E30 320i of 1985 vintage. Excellent car overall. Only niggle in 11 years of ownership was a dodgy FPR that took months to diagnose and was fixed in minutes with a 10 quid second hand one off of ebay :)
Scrapped it recently even though it was running happily. Getting a bit rusty, and I just didn't need it any more. Had hoped it could be used for banger racing but apparently it's too big/powerful/whatever :(
Al.
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Huh ! They used to race anything as bangers at my local stadium. I recall a guy called Sooty Seaton who used to race an old Jag with stacks up through the bonnet. I suppose the Elfan Safety mob have now decided it's too dangerous in case a BMW crashes into a Fester during one of the Demolition Derby type races that use the x-over in the centre of the track ... :-\
Arfa
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Al wrote:

Posted reply from google account and it showed a different user name so contributers may not have noticed my reply;
My car is a Nissan Micra.
Geoff Lane
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on 23/02/2009, Geoff Lane supposed :

The very basic fan speed controllers use large wirewound resistors to control the speed and these often burn out or develop poor connections. If your a/c runs the fan on its lowest speed without you needing to alter the fan speed setting, then that might indicate a fault on the switch or wiring from switch to resistors. Either way look for charred or discoloured connections.
A more sophisticated system for fan speed control uses a pulse width modulated controller instead of resistors and these are usually fitted on the climate control type of system.
--
Regards,
Harry (M1BYT) (L)
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