Sounds like an incompetent dealer. Take it to another MB dealer. Evaporator never go bad... the reason is it is in protected area where you can't accidently smash it.
MB did have evaporator problem but only on W140 big older S class but they learned their lesson and was a manufacture defect. I have not heard problem on W210 yet.
The sensor is located on the driver side under the dash near the center dash area. You can't take it out without evacuating the A/C system of freon... MB dealer has that proprietary diagnostic computer to check what is wrong with A/C system.
The evaporator sensor problem is usually accompanied by a "locked" EC mode... that you can't turn of... red lite on EC button is always on.
Driver side and passenger side has it's own temperature setting...
In any case, do not let them rob you of your precious money.