I'm pretty sure this still has the older heater control that goes back to 95 or so. ( long thin display, buttons all around )

With the key on or engine running, turn the fan to low. Press and hold the " REST " button and wait. The display will go to a data screen flashing a 01 then another number. Use the fan - and + buttons to scroll through the screens ( 02 , 03 , 04 ) Engine coolant temp is somewhere in the 05 to 09 range.

If the coolant temp is showing a believable temp, changing the sensor won't fix your problem. There is only one coolant temp sensor, it is connected to the engine computer then data sent over CAN bus to trans . HVAC , dash.

You can also get diagnostic info with other buttons. The type of control was used on most all MB from 95 to 01 or so. They do not directly interchange as the E and S had split temp and the C / SL single temp.