My A/C is not functioning properly. The fan and compressor seem to work only at certain speeds or rpms. At stationary, no fan noise or cooling can be heard or felt. After I have accelerated a distance, it comes on and when I release the accel. it goes off and comes on again when I step on it. Funny or normal??? The windscreen takes ages to clear so the system is not dehumidifying quickly enough and can be dangerous. Can't wait to move off for too long. At the most 3 minutes from engine start, more and it will seem like somethings very wrong. The heater function is working. A/C is not very cold, not enough anyway. What can be wrong with it besides the drier tank glass window at the top having a crack in the glass right across, but with no moisture leak apparent.

1994 Euro C180 Elegance auto.
194,000kms.
Otherwise running fine.