To start with welcome..

That chassis is a W201..that a/c system uses a heater valve that is either OPEN or closed & then mixes air thru a blend air door. Vacuum controls the blend air door & the heater valve. IF vacuum if removed from heater valve the inside OUTER & foot well vents should get HOT. IF not then the heater valve OR heater core would be the problem..

The sampler motor(aspirator) for the in-car temp sensor on a 1986 car is behind the dash vent on the passenger side. ON a 1987 & later car it is in the dome lamp assembly.

__________________
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