I have a problem with my aircon but my mechanic just emailed this in

 

"Although it could be something else electronic in there that's overheating and shutting everything down. By the sounds of it tho, it is something to do with the speed reduction circuitry (i.e. boost is flat chat, 1,2 & 3 are ""reduced"" or limited speeds).

Replace the resistor as suggested, and see how things go. If you've still got a problem, I'd be checking the electonics of the control system more closely. Depending on your electronic experience, it might be time to visit Ford or an auto electrician..."
 

details on car? and what are the symptoms of a/c problem. (seems like the blower fan?)