Gilly,

I have a couple of problems with the ACC on my 1990 500SL (R129).

1) I cannot seem to get it into diagnostic mode.

2) Air only comes out of the defrost and side vents

The compressor is operating normally, high/low sides are good and steady. Is it possible that the pusbutton unit is the cause of both these problems, or am I looking at replacing the switchover valve too?

Thanks,

-Dennis