Hi,
some feedback: after a diagnostic with the T4 the thermistor evaporators came up with an error. I changed the two thermistor evaporators (part no JQC000040) and toped up cooling fluid. The AC is working fine since then. I bought an aircon ECU (B28) (part no JFW000011) for safety from smc343 on ebay too, but it really seems to be that one of the sensors was the problem. Hope that's it.
sensors.jpg
Thanks a lot to all of you for your time and help to this annoying problem.
Ciao
Marcus