Hello, I am looking for some help with this issue on a 2008 C180 Kompressor. I have searched many threads but been unable to find a solution or at least a way of diagnosing my issue definitively.

The cooling fan starts running on a cold engine a few seconds after start up. It only goes off when the engine is switched off. The AC does not work. Diagnostics shows AC over pressure. Temp readings are correct.

So investigated the AC pressure switch (the one in the front at the bottom of the radiator) I have found that with the connector removed from the sensor both the signal and supply wires are at 4.88V. The signal and supply wires are not shorted. I measure M ohms between them. So I am thinking my problem is caused by something putting 5v on the signal wire causing the diagnostics to think the AC is over pressure.

The pressure sensor itself measures 80kohms between signal and supply pins so I am thinking this is OK. The fan module appears OK and as far as I can tell behaves as normal.

Can anyone supply a circuit diagram of the AC system? Has anyone seen a similar issue.

Any help would be much appreciated
Thank you

 

Anyone out there?