An incredibly common problem, not the Aircon though! It is caused by the pollen filter cowl not being sealed correctly, it's the bit in front of the passenger side wiper. Have you had it serviced recently? Sounds like they didn't seal it properly if so go back and get them to remedy it f.o.c. Alternatively, you can do it yourself with some butyl tape, available from ford. 1. Remove centre screw cover-simple clip off. 2. Run fingers under the screen edge of the panel to release the butyl tape. 3. Open bonnet and release the clips along the bulkhead-press in the tag and lift up. 4. slide the panel towards the center of the car-to remove the panel and leave the clips in situ on the metal panel under the screen. To Refit the scuttle panel 1. release clips from the bodywork- press inwards the two outer tags of the square clip that is in the bodywork and remove both parts of the clip as one piece. 2. Remove all traces of the old butyl tape from the under side of the scuttle, this should mostly peel off you may need a little white spirit or similar to remove all traces. 3. Renew the butyl tape. 4. slide the clips back into their locating pionts on the under side of the scuttle. 5. clean the bottom edge of the windscreen. 6. Lift the panel back into place locating the square clips into their square holes in the bodywork, clip the bulkhead clips into place and apply light pressure along the line of the butyl tape. 7. Replace center screw and cover. The trick is to remove both halves of the clips from the bodywork and clip them together before assembly. Trying to push the male and female parts of the clip together whilst the female part is still in the car is where most of the trouble arrises, as it is very hard to line up without being able to see it