The evaporator temp sensor "feels" the temperature of the A/C evaporator, & can cause the Pushbutton control to cycle the A/C compressor so that the evap doesn't freeze up.
Common failure here in the SOUTH.

__________________
MERCEDES Benz Master Guild Technician (6 TIMES)
ASE Master Technician
Mercedes Benz Star Technician (2 times)
44 years foreign automotive repair
27 Years M.B. Shop foreman (dealer)
MB technical information Specialist (15 years)
190E 2.3 16V ITS SCCA race car (sold)
1986 190E 2.3 16V 2.5 (sold)
Retired Moderator