Automatic Air Conditioning (AAC), Function

GF83.40-P-0001P Automatic Air Conditioning (AAC), Function

MODEL 203.0 /2 /7 up to 31.5.01
- with CODE (580) Air conditioning (or Tempmatic for USA)
MODEL 203.0 /2 /7 as of 1.6.01
- with CODE (580) Automatic air conditioning
- up to Model Year 8
MODEL 203.0 /2 /7 as of 24.4.04
- except CODE (581) Comfort automatic air conditioning
- up to Model Year 8

The automatic air conditioning (AAC [KLA]) regulates the desired interior compartment temperature in accordance with the driver or front passenger needs in terms of heating, cooling, and air distribution.
The automatic air conditioning (AAC) is operational immediately after the engine is started and produces the last stored temperature- controlled condition before the vehicle was locked. The system operates depending on air humidity (up to 28.6.06) and air 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 (AAC [KLA]) regulates the interior temperature separately for the driver and the passenger-side.

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 window fogging, the footwell flaps are opened fully for approx. 30 seconds after the ignition has been switched on. When the ignition is switched off, the fresh air/air recirculation flap is automatically moved into a 50 % fresh air and 50 % recirculated air position. This achieves a significant reduction in the flap closing forces.

Heating circuit
The coolant is heated by the engine. Afterwards, it passes through the heater heat exchanger, from where the heat is delivered to 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.
Coolant is always flowing through the heater heat exchanger. Temperature control, depending on the temperature desired in the vehicle interior, is carried out via the blend air flaps, which are activated - separately for the left and right side - via the left (M2/6) and right (M2/7) blend air flap actuator motor.

Refrigerant circuit
The refrigerant compressor (A9) compresses the gaseous refrigerant, which causes it to heat up. The refrigerant is passed on to the condenser and thereby cooled down. After being cleaned in the fluid reservoir, the liquid refrigerant is injected into the evaporator. The refrigerant evaporates and cools down. The refrigerant compressor (A9) again intakes the refrigerant, which has returned to its gaseous form as a result of heat absorption.

Automatic air conditioning (AAC [KLA]) control
The electronic control of the automatic air conditioning (AAC [KLA]) takes place using various components 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.

Temperature control
The desired temperature is achieved or maintained at a constant level by cooling or heating the air. For a more accurate temperature control, the temperatures of the evaporator, the outside and inside air are read in.

Residual engine heat utilization (with code (450) Taxi version or code (670) Residual engine heat utilization system (REST [MRA]))
The residual engine heat utilization permits to heat the vehicle also when the ignition is switched OFF. The system uses the residual heat of the engine's coolant to accomplish this.