AC ... Not so cold!!

[Marc-1]

1991 300SL
When I turn the AC on and set the temp control to 60 deg. outside temp air comes out of the drivers side vents and heated air comes out of the passengers side. This car doesn't have independent climate control so what's going on here??? I tried pushing all the buttons on and off, up and down thinking something is stuck but to no avail. Can anyone help me? It's getting hot here and I need to figure something out )
Oh, in front of the car, right in the grill area there is a valve, is this where the AC is charged? How much pressure should there be in this particular car? Is the freon 134R?
Please enlighten.... Thanks

[bobterry99]

The car is R-12 unless it has been converted. The fitting at the front is the high-pressure side, so you don't fill the system from there. The low-pressure fitting is located close to the brake booster. I don't know the pressure specifications.

Have you run diagnostics as explained here? What temperature readings are being fed to the controller?