I have just replaced the climate control unit due to the original's buttons broken and failing, the air con is working ok.
I found one second hand £150 (new Merc price £470) had it sent to me in the post, it works perfectly apart from the air con cooling fans run all of the time when the engine or ignition is on, even with the air con off, no fault codes were registered when It was scanned.
When I put the old unit back in it was back to normal, so it is the unit problem, is it faulty or as it has been mentioned to me does it need programming to new car, as it is set up for the car it once belonged to.
Any help appriciated
John