There are three different Climate Control systems for the 300 123
series vehicles. Does your car have a wheel with numbers on it to the
left of the buttons? A wheel that has degrees Celcius on it? If it
does you have type III, which is what my car has.
On type three, the automatic climate control system, the buttons are,
from left to right:
All vents open, for clearing the dust out, should be used for at least
5 minutes, monthly
AC and dehydrated heat
Economy heat (no AC engaged)
The buttons to the right of the five button center group provide
manual control of the fan speeds. Most of the time you should have
the small button in the middle engaged as it is for the automatic
setting. I think there are seven different fan speeds on automatic,
but just two, slow and fast, on manual.
If you have type III and all the vacuum controls are working it is a
miracle! But they can be diagnosed and repaired. I have my dashboard
out for the 3rd time right now as I have had another vacuum failure
under there somewhere.
If you e-mail me at email@example.com I will send you the vacuum
diagram for your car. I need the year and model.