A/c Problem On A4

[vserghi]

I have a problem on my A4 where, if I am sat idling at traffic lights say, the A/C will switch itself off, if I am driving then all is Ok.

I went to a garage for them to have a look at the system, and they said that apart from the refrigerant being 200g down (hadn't been checked in the 4years since I had the car), the electric cooling fan was not starting as the pressure rose (i think it went up to 350psi!). This leads me to think that either the electric fan is on the way out or the thermal switch in the radiator is playing up. When the A/C is on and I'm at idle, the compressor will make a strange noise if I blip the throttle. Now the car has done 122,000miles, so if the A/C is reaching those high pressures I'm not suprised it makes funny noises.

So the question is, what would be the most likley culprit, the switch in the radiator, or the fan. The crappy Haynes manual does not supply a circuit diagram for the cooling fan. I have considred replacing the compressor, but that is a hefty £250 part. If I can get away with changing the switch or fan, the better.

Any help, or suggestions?

Vas.