when i press the airconditioner or dehumidifier buttons of my 190e2.6, with the fan turned on, the airconditioner compressor does not engage (the vented air remains warm and there is no additional load on the engine, as seen from the vacuum gage while at idle).

i've checked the fuses and everything seems to be fine.

i understand that there is a thermostat in the evaporator that is also in the compressor electrical loop. How do i check this, or is it best done by a mechanic?

are there other things that i should check, before i bring the car in?

thanks.