Jim

"lennario" <dave_lennon@fsmail.net> wrote in message
news:be9517c8.0503021252.1a543c9a@posting.google.com...
> We have recently bought a 5 year old Focus and it has just developed a
> fault with the heater. It only works on number 3. Does anyone have any
> idea what may have caused the fault and whether it might be easier to
> fix?
>
> Thanks

from an earlier post

There is a resistor network with a thermal fuse associated with the
switch that sets the fan speed. If the thermal fuse goes open circuit
then the three lower fan speeds are dead but the fastest setting still
works.

lennario

Thanks very much for the advice, much appreciated. I should have made
it clear that the blower only works on the second fastest setting
(number 3).

I will take the advice on board and investigate further.
Thanks again.

Alan <junk_news_a@amacleod.clara.co.uk> wrote in message news:<K9YmVVGazjJCFwoa@amacleod.clara.co.uk>...
> In message <be9517c8.0503021252.1a543c9a@posting.google.com>, lennario
> <dave_lennon@fsmail.net> wrote
>
> >We have recently bought a 5 year old Focus and it has just developed a
> >fault with the heater. It only works on number 3. Does anyone have any
> >idea what may have caused the fault and whether it might be easier to
> >fix?
>
> Do you mean the heater or the blower fan.?
>
> If you mean that the blower fan only works on the fastest setting then
> it may be an easy DIY fix if you have some skill with a soldering
> iron/gun and a multi-meter.
>
> If the fan only works on the fastest speed there is a good chance that a
> thermal fuse has failed. Unfortunately the thermal fuse is part of the
> blower resistor assembly.
>
> Note: The thermal fuse is different to those fitted in the fuse boxes.
>
> The speed of the fan in the first three positions is controlled by a
> bank of resistors which are relatively large and get hot. The thermal
> fuse is in series with these resistors and physically almost touching
> them. When the fuse blows the first three position don't work. In the
> final switch position the battery voltage goes straight across the
> motor, bypassing resistors and thermal fuse network, hence it works.
>
> The resistor and fuse assembly is usually mounted in the blower motor
> air stream and I believe that you can get to the resistor assembly by
> removing the blower motor in the Focus. Release the glove box by flexing
> the back plastic sides (a _tiny_ bit of force may be required). The
> glove box then hangs out of the way and you can see the blower motor and
> fixings.
>
> Below is what I have advised before but it is worth getting a second or
> third opinion from the news archives at Google groups.
>
> <http://groups.google.com>
>
> Type 'thermal fuse blower motor' into the search box (without the
> quotation marks).
>
> The advice given for other cars is valid.
>
> The fuse is a two legged device which when it reaches a preset
> temperature blows permanently open circuit.
>
> I would assume that the way the module is constructed that the fuse
> alone isn't a replaceable part and that a dealer would charge for the
> whole module. However it is a do-it-yourself fix if you can find the
> motor 'resistor module' and have some basic electrical soldering
> capabilities.
>
> In the UK the a replacement thermal fuse (for the do-it-yourself repair)
> can be obtained quite cheaply (0.5 GPB or less than $1 US) from
> electronic component stores.
>
> <http://www.maplin.co.uk/>
>
> or
>
> <http://rswww.com>
>
> I've included the references to the devices plus a circuit of the blower
> motor circuit on
>
> < http://www.amacleod.clara.co.uk/focus/index.htm>
>
> When buying the replacement fuses the one you want is probably towards
> the higher end of the temperature range (150+ degrees C).
>
> Before replacing the thermal fuse check it with a meter to see if it
> open circuit or temporality short across it to see if the motor works on
> the lower speed settings.
>
> Despite the warnings about not to solder to the leads of a thermal fuse
> I've successfully used a high wattage soldering gun and _quickly_
> soldered at the ends of the leads. Obviously as it is a one time thermal
> fuse leaving the soldering iron in contact too long will heat up the
> whole device to a temperature where the fuse blows. As they are cheap it
> may be worth ordering a couple - just in case :) You could attach a
> crocodile clip or bulldog clip as a heat-sink to the body of the fuse
> while soldering to reduce the heat build-up.
>
> Cut the old thermal fuse out but leave about quarter of an inch of the
> lead on each side that is crimped to the terminals on the assembly.
> Leaving a bit of the old lead in place will make soldering the new
> component easier. Soldering to the terminal post is difficult unless you
> can clean it up with a small file.
>
> The problem may have been caused as a result of water getting into the
> system and the blower motor not running as smoothly as it should. On
> previous cars where I have fixed identical problems the motor shafts
> were rusty and some lubrication (ONE DROP of engine oil from the
> dip-stick) was applied to the motor shaft bearing area.
>
> Also consider that it is not unknown for the switch to mechanically
> fail.