The buttons are, from left to right, defrost (full heat, all the air to the windshield), split flow (some air to floor and to windshield all the time, nice for winter driving), full automatic floor/dash vents (no defrost flow), EC (economy -- works like the previous button but without the AC compressor) and ) for OFF.

There are three vertically arranged fan buttons -- bottom is low (don't use this in really cold weather, you feet may freeze from low airflow), auto, and high.

There is some "float" on the temp setting -- my 300D tends to run a bit cool, so I sometimes have to set it warmer a few degrees on cool days to keep cold air from blowing on me. Less of a problem on EC since the AC isn't running with reheat. Small adjustments are needed from time to time.

If you still have poor temp control, or the unit switches modes constantly with contant operation of the switchover valves (lots of clicking noises from the dash), the pushbutton control unit needs to be resoldered or, if that doesn't fix it, replaced.

Peter

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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!