Fault: On a Ford Focus the cabin blower only works on position 4 (full speed). On settings 1, 2 and 3 the motor doesn't work.
The probable cause of the fault is that the thermal fuse in the blower motor resistor/controller pack has failed. The thermal fuse is a heat sensitive fuse that goes permanently open circuit when it reaches a certain temperature. In the fastest speed switch position the blower motor is connected directly across 12V bypassing the fuse (see diagram below).
Less likely, it is not unknown for the switch to mechanically fail but this often gives no operation on only one or two positions. To remove the switch you first have to remove the radio. There are screws holding the top of the fascia with switch just inside the radio compartment – the bottom of the fascia clips off after you have released the top.
Ford Focus blower speed control module - found behind the glove box and close to the blower motor. It is reported that newer modules are black in colour rather than blue
The thermal fuse is the silver component on the far right of the photograph (on the two legs)
The 3 resistors are encapsulated within the big green mass seen in the middle of the module.
Release the glove box by flexing the sides (with a tiny bit of force) and pulling forwards.
View of what is behind the glove box in a UK (European) Focus. In a US model the fuse panel will be situated elsewhere (behind a panel in the driver's footwell?)
It is reported on the Internet Newsgroups that a replacement module cost less than 20 Dollars in the USA, less than 20 Euros in continental Europe and around 20GBP from Ford dealers in the UK. Fitting will be extra - my local Ford dealer charges 80GPB per hour (around 150 Dollars US). Replacement of the module should be a fairly easy Do-It-Yourself job.
If you have some experience with electrical/electronic soldering iron there is a more cost effective repair. In the UK a replacement thermal fuse can be obtained for around 0.5 GPB (1 dollar US) from electronic component stores.
For example Maplin or RS Components
See below for some sample pages showing the type of fuse required.
Before replacing the thermal fuse check it with a multi-meter to see if it is open circuit or temporarily short across it to see if the motor works on the lower switch settings.
When buying the replacement fuses I've previously guessed that the one I needed was towards the higher end of the temperature range (150+ degrees C). I recommend that you check in the Internet News Archives at http://groups.google.com/ for further information. Search for “thermal fuse blower motor” and the advice given for other car makes/models will be valid.
Cut the old thermal fuse out but leave about quarter of an inch of the old 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 LOT easier. Soldering to the terminal post is VERY difficult unless you can clean it up with a small file.
Despite the warnings about not to solder I've 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 or bulldog clip as a heat-sink to the body of the fuse while soldering to reduce the heat build-up.