Aircon blowing Hot 'n' Cold (W203)

[jon pollard]

With A/C dials set to the left the aircon on my C-Class (W203) has decided to blow cold through the left vents, warm down the right and a mixture through the middle. The presence of cold air suggests to me that gas is OK (system re-gassed not long ago) and that the fault is a sensor or valve problem. Any ideas???

 

[jberks]

Absolutely - if you have cold air on one side then the aircon is fine.
Id suspect a duff duovalve - controlled by the switch and ambient temp sensor. Assuming that both temp switches are set to the same position then either the switch is faulty or the duovalve. I've heard of stuck valves, faulty switches are rarer. The test is the same anyway, check the current to the valve, disconnect / reconnect and see if the temp changes, perhaps swap the feeds between the 2 sides of the valve and see what happens.
Do a search for duovalve - there are lots of discussion though mainly on W123 and W124s but I think the technology is basically unchanged.