I'm trying to understand and fix the climate control on this '85 300D turbo that I picked up recently and am restoring to be a daily driver.

I've not yet found a user manual for this type of climate control. It is significantly different from my '83 240D.

The fan on/off switch works, but when I press "auto", the fan stops. When the fan is running, I get hot air at all times.

I've not noticed the push buttons doing anything at all except the right most one with the "0", which turns off the fan.

I'm guessing that the buttons, left to right are:
send air to defroster,
send air to floor and dash,
send air to floor only,
send floor to floor and EC?? - no idea
turn off

And, how is the "auto" button supposed to work?
And, is there a way to vary the fan speed?

So first, I need to understand how the controls are supposed to work, and then set about fixing.