Dave_lennon 2011-11-04 15:29:32
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
Jim 2011-11-04 15:29:39
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
Alan 2011-11-04 15:29:45
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
Below is what I have advised before but it is worth getting a second or
third opinion from the news archives at Google groups.
Type ‘thermal fuse blower motor’ into the search box (without the
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
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.
I’ve included the references to the devices plus a circuit of the blower motor circuit on
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
Dave_lennon 2011-11-04 21:14:34
Thanks very much for the advice, much appreciated. I should have made
it clear that the blower only works on the second fastest setting
I will take the advice on board and investigate further.
Alan 2011-11-04 21:14:37
Previous posts to this newsgroup have said that the switch itself can
If one speed setting works then the fuse in the fuse box is OK
If one of the three lower speed settings work then the thermal fuse is
If the fuse in the fuse box is OK and the fastest speed setting doesn’t
work it suggests a faulty switch.
My Haynes manual  for a UK Focus suggests to get at the switch
Disconnect the battery (for safety reasons)
Remove the radio/cassette
Undo the four securing screws from inside the radio/cassette player
aperture, then carefully unclip the heater control panel from its three
retaining clips in the fascia.
Disconnect the wiring connector from the switches as the control panel
is being removed. 
digit security code (and instructions) that you need to enter to make
the radio work again. Radio Removal
It has been suggested that the ‘special tool’ for removing the radio can
be fabricated from a couple of wire coat hangers.