The heating, ventilation, and A/C (HVAC) system in the M-Class has semiautomatic temperature regulation and manual control over the air source and distribution. The temperature control is achieved without the use of a heater valve, also called mono valve in other models. The M-Class heater core is thus always hot, at about 87 deg C. Air Conditioning Switch The On/Off switch connects to the A/C control module (N19), which, through the All Activity Module (N10) controls the activation of the air conditioning compressor clutch. The A/C compressor operates only when the engine is running and the blower motor is switched on. The AAM (N10) also uses other information from the CAN to choose when to operate the compressor clutch, i.e. engine temperature. Air Temperature Control An NTC resistor behind a grille below the low range switch senses the in-cabin temperature. A hose connects it to the main climate box thus drawing air across the sensor. Air temperature is ...