Rear Air Con

[ccredlaw]

On my 2004 E320 CDI Saloon, the rear air conditioning unit has started to pump out hot air after a few miles. The front is fine and pushes out cool air as normal. All four temp thermostats are set the same ie 20 degrees C for both front and both rear.
Air con was checked a couple of weeks ago during a normal service.

Any pointers as to what the problem is would be most welcome.

 

[Oarsman]

It sounds like the duovalve is stuck in the open position, allowing a constant flow of hot water through the rear heater matrix.