atikovi,

Your levers for heat and air flow direction are a little off. The icon with the layout for the defrost mode should have the heat on full, which has the two heater levers in their outward position, and all the air going to the windshield, so one lever is all the way outboard (the one with the arrow pointing upward) and the other all the way inward (the one that directs air flow to the footwell, which minimizes flow in that direction). It looks like your heat and flow direction knobs on the levers have been reversed.

The round knob between the levers with the word defrost on it is the fan control. The fan must be atleast in the first speed to turn the compressor on. Otherwise it is probable the air cooler will freeze up and no air will come in.

The knob you have that is broken is the airconditioning temperature selector knob. The rule for all these symbols is you move the control in the direction of the icon feature getting thicker to get more of that feature and in the direction to get less. In the case of the defrost knob, the intent is that the defrost position is at the end of the full thickness of the blue curly icon. Meaning when you turn it all the way the fan is on all the way and presumably you would only do that to make the windows defrost.

The airconditioning temperature selector knob runs the same way, as you need more cooling you turn it in the direction that makes the icon symbol a thicker blue curly shape.

I would think you can dope out if someone took the heating and flow direction knobs off by turning the fan on and fiddling with the flow direction (blue lever knobs with arrows at the thick ends pointing up or down) and heat levers to see which ones make the air go up on the windshield. Once you get these straightened out you should be able to maximize cooling by shutting the heat off all the way, and turning the air conditioning all the way up when you replace the knob that is broken off.

Hope this helps, Jim

__________________
Own:
1986 Euro 190E 2.3-16 (291,000 miles),
1998 E300D TurboDiesel, 231,000 miles -purchased with 45,000,
1988 300E 5-speed 252,000 miles,
1983 240D 4-speed, purchased w/136,000, now with 222,000 miles.
2009 ML320CDI Bluetec, 89,000 miles

Owned:
1971 220D (250,000 miles plus, sold to father-in-law),
1975 240D (245,000 miles - died of body rot),
1991 350SD (176,560 miles, weakest Benz I have owned),
1999 C230 Sport (45,400 miles),
1982 240D (321,000 miles, put to sleep)