Slightly OT: not to do with smells in Air con, but to do with the above comment: We had a Ford Galaxy, that had a similar warning in the handbook, just before we sold it, we found out why. Apparently, we hadn't run it enough, and the compressor seized. Since the fan-belt drives this compressor the whole time (even when the air-con isn't on), this was making a burning smell as the belt was forced over a fixed pulley. Cost >£1000 to fix (20% of the value of the car). Another one from the Ministry of crap design.
Tony.