No, I get heat, defrost, and AC through the vents. In the summer I put a rolled towel on the vents to prevent fogging the windshield; this gives full air through the ac vents. In winter I remove the towel for heat and defrost.

Mercedes tech told me to try to reset memory. Step 1 - roll thermostat to highest heat and punch each button from left to right starting with defrost. Step 2 - roll thermostat to highest AC and repeat punching buttons in same order. Did not work but my flaps have not closed for over five years so maybe memory is not the problem.

So I must assume the vac switchover valve is not operating to open and close the defrost flaps. But not sure.