interior fan

Slightly applicable, had this happen in a Nissan. There's a sort of 'card' in the Nissan that acts as a resistor at the various settings, thus limiting the current to the fans, making them blow less.

Maybe something similar in the Focus as gone? Figures.

Just fixed this on my 2001 X3 (US model) for about $15.

You will have to remove the glove box. To the left of the blower housing you will see a couple of wires running to a blue or black plastic rectangle about 2" by 1", mounted to the fire wall with one bolt, if I remember right. This is the piece you need to replace, called a variable resistor, I believe. I was told this is a dealer item only, so go to your dealer's parts counter. If you lose your high speed before you get this fixed it is probably a fuse in the engine compartment as well. Your owners manual will tell you which one. UK models may be a different setup. Someone earlier in here said the resistor (thermal fuse) was in the blower housing. I don't know about that. Google thermal fuse for this group and find more on the topic.

In message , hewden wrote

The most likely cause is that the thermal fuse in the ventilation motor resistor pack has blown. The speed of the motor is controlled by three resistors with an in series thermal fuse. The fourth position (full speed) just switches the motor straight across the 12V - with no series resistors or fuse.

See

It is not unknown for the switch to mechanically fail but this is less likely.

Previously posted is the DIY method of fixing....

In message , EOO wrote

I've posted the link to the thermal fuse but if the combined part with the resistors and thermal fuse is only around 8 pounds for a D-I-Y fix then that may be the quickest option. My experience with Ford UK dealers suggests a part in the US costing $15 with be at least ten times that price in the UK.