Automatic air conditioning (AAC), function - GF83.40-P-0001Q: Notes

Model 209.3 /4 except CODE (581) Comfort automatic air conditioning 

Function 

The (AAC) automatic air conditioning regulates the desired passenger compartment temperature in accordance with the driver or passenger needs in terms of heating, cooling and air distribution ducts. The air conditioning is fully operational after starting the engine and restores the last stored temperature status before locking the vehicle. The system operates on the basis of the humidity and temperature. The ambient air is first cooled down by adding cooled air from the evaporator, even at low outside temperatures, and then passes through the heater heat exchanger where it is heated up to the desired interior temperature. The automatic air conditioning regulates the passenger compartment temperature separately for the driver and passenger sides.

The automatic air conditioning utilizes the signal of the outside temperature display temperature sensor (B14) together with the air humidity sensor (B31/2) integrated into the A/C bus as input signals for calculation of air distribution, temperature control and blower motor regulation. The evaporator temperature sensor (B10/6) measures the temperature at the evaporator air outlet.

The interior temperature is measured by the in-car temperature sensor (N22b1) in the AAC control and operating unit (N22).

For vehicles as of 1.6.05, the interior temperature is also determined by the in-car temperature sensor (N70b1) in the overhead control panel control unit (N70).

The automatic air conditioning (AAC) function can be summarized under the following list of subfunctions.

• Ventilation 

  Ventilation ensures aeration in the vehicle interior. Ventilation is achieved with the support of the blower motor (A32m1) during normal operation, when vehicle is stationary or to increase the air flow. The air is distributed in the vehicle interior via air distribution flaps.

  In order to prevent windows from fogging, the footwell flaps are opened fully for 30 seconds after the ignition has been switched on. When the ignition is switched off, the fresh air/recirculation flap is automatically moved into a 50 % fresh air and 50 % recirculated air position.

• Automatic air conditioning temperature control 

  The desired temperature is achieved or maintained at a constant level by cooling or heating the air. An exact temperature control is achieved by the reading in various temperature sensors.

• Automatic air conditioning control 

  Control of the automatic air conditioning takes place using various control units that are interconnected via the Controller Area Network bus class B (interior) (CAN-B). The CAN-B is a bi-directional bus, i.e., each connected control unit receives and transmits information.

• Heater circuit 

  Coolant is heated via the engine. The heated coolant is subsequently guided through the heat exchanger, where the heat is emitted into the air in the interior. Via the heater return, which contains the hot water recirculation pump (M13), the coolant is returned to the coolant pump.

  The hot water recirculation pump (M13) ensures that the coolant is circulated.

  The coolant flows through the heating system heat exchanger permanently.

  Temperature control, depending on the temperature desired in the vehicle interior, is carried out via the blending air flaps, which are activated - separately for the left and right side - via the left (M2/6) and right (M2/7) blending air flap actuator motor.

• Refrigerant circuit 

  The refrigerant compressor (A9) compresses the refrigerant vapor which is heated up during the process, routed into the condenser and thus cooled down. After being cleaned in the fluid reservoir, the liquid refrigerant is injected into the evaporator. The refrigerant evaporates and cools down while doing so. The refrigerant compressor (A9) again intakes the refrigerant, which has returned to its gaseous form as a result of heat absorption.

• Engine residual heat utilization system (only for code (670) Residual engine heat utilization system (REST)) 

  Residual engine heat utilization enables the vehicle to be heated even when the ignition is OFF. To do so the system utilizes the residual heat from the engine and leads it into the passenger compartment via the blower motor (A32m1). The hot water recirculation pump (M13) ensures that the coolant is circulated.