[arcticpiper]

I just got back from a (hot) weekend away and had exactly the same problem.
The outside temp was around 28deg C and with the A/C set at 18deg on auto it would work for an hour then the system stopped cooling and the fan speed dropped right down. Hitting the max button had no effect. I eventually turned it all off and sweated for 15mins then turned it back on to auto again and it started working again. On a 6hr trip this became very annoying. Phoning the dealer again today - it's already had a camshft replaced and the central door locks - very disappointed with my first BMW.............

Got a call from the dealer - they say it's the Evaporator Valve which has a tendency to "freeze up" when the A/C is being used to the max. Part on order - car off the road for two days.