Following my first experience of this my car was taken to a garage. They were unable to pinpoint the problem, and found the fact that the fan speed sometimes changing extremely puzzling. They asked me to return once the system had completely broken so they could nail the exact component that had failed.

Weeks if not months have now past. This morning, the temperature rose of it's own accord. I switched the fan off as I usually do at this point.

Then, the fan kicked it and decided to blast hot air at me. Only control I had was to increase the fan speed or open the windows - thank god it wasn't raining!

Any ideas? Garage reckons the temperature is one motor, the fan speed another. The two are isolated and thus it's very strange that they should behave as though they may be connected.

The car has been hooked up to the garage diagnostics but it apparently wasn't very specific - a short circuit but no actual motor having blown.

Have they a common earth point?