Automatic air conditioning (AAC), function - GF83.40-P-0001SX
MODEL 216.3, 221.0 /1 up to Model Year 8
Function
The automatic air conditioning (AAC [KLA]) regulates the interior temperature selected by the driver and the passengers. It is designed as a two-zone air conditioning.
Immediately after engine start, the last temperature condition set before the vehicle was locked is restored.
The AAC [KLA] operates depending on the air humidity and the air temperature. Even at low outside temperatures, the ambient air is first cooled down by cooled air from the evaporator, it is then routed through the heat exchanger where it is heated up to the desired interior temperature.
Heating circuit
Driven by the coolant pump, the coolant circulates in the engine cooling circuit. In the process, it absorbs engine heat.
After the engine has reached operating temperature, the air conditioner water valve (Y19/2) is opened upon actuation by the AAC [KLA] control unit (N22/1). The heated coolant passes through the heater heat exchanger, which dissipates heat to the air blowing by. Additionally, at low engine RPM, the coolant circulation pump (M13) is actuated to ensure that the flow volume needed to heat up the air blowing by is adequate.
Refrigerant circuit
The refrigerant compressor (A9) driven by the engine compresses the refrigerant vapor which is cooled down in the condenser. As it cools down, the refrigerant liquefies. The liquid refrigerant is then injected via the expansion valve into the evaporator where it evaporates. It cools down during the evaporation process and withdraws heat from the air blowing by, cooling it down. The refrigerant compressor aspirates the refrigerant which has turned gaseous on account of the heat absorption and then compresses it yet again.
Control
Electronic regulation of the automatic air conditioning (AAC [KLA]) is performed by way of various components which are networked over the interior CAN, the chassis CAN, the telematics CAN, the central CAN, the AC bus and the AC LIN. The desired temperature is achieved or maintained at a constant level by cooling or heating the air.
Ventilation
The ventilation system prevents windows from misting up, supplies air to the occupants and ensures that uniform and pleasant temperatures in the interior are reached quickly.
Ventilation is achieved with the support of the blower motor (A32m1) during normal operation, when vehicle is stationary or to increase the air flow.
Engine residual heat utilization system
The residual engine heat utilization feature makes it possible to continue to heat or simply ventilate the vehicle with circuit 15 "Off" or circuit 15C. For this purpose, the residual heat of the engine is used. Pressing the OFF/residual heat button (N72/1s38) activates the function. The coolant circulation pump delivers the coolant that is still warm through the heater heat exchanger. The air drawn in by the blower motor is routed along the heater heat exchanger and thus heated up.
During residual engine heat utilization, the blower motor is actuated with a lower output. The function is terminated after a specific time has elapsed or when the on-board power supply voltage drops.
With code (582) Rear air conditioner, coolant is delivered through the rear heater heat exchanger by the rear auxiliary heating system delivery unit (A31/1).
Actuation of the coolant circulation pump, of the blower motor and of the rear auxiliary heating system delivery unit takes place via the AAC [KLA] control unit (N22/1).
AC-OFF function
This function blocks the refrigerant compressor's cut-in. This function can only be operated via the front central operating unit. An active AC OFF function is shown in the COMAND display.
Operation
The AAC [KLA] is operated via the upper control panel control unit (N72/1) and the front central operating unit (A40/9). The settings made via the front central operating unit are shown in the COMAND display (A40/8).
The following functions can be operated via the upper control panel control unit and via the front central operating unit:
- Switch off the air conditioning
- Defrosting (Defrost)
- Preselection of the interior temperature and blower setting, separately for the left and right sides
- Adjustment of the air flow to focused (high air flow), medium (default setting), diffuse (low air flow)
The following functions can only be operated via the upper control panel control unit:
- Overall automatic system separately for the left and right sides
- Air recirculation mode
- Switch off climate control
- Activation of the residual engine heat utilization with ignition switched off
The following functions can only be operated via the front central operating unit:
- Air distribution separately for the left and right sides
- Adaptation of the footwell temperature
- Coupling of all setting zones with driver zone "MONO"
- Resetting all climate settings to the manufacturer default setting
| Automatic air conditioning (AAC) component locations | GF83.40-P-0001-01SX |
| Automatic air conditioning (AAC [KLA] block diagram | GF83.40-P-0001-05SX |
| Refrigeration cycle function | GF83.40-P-2001SX |
| Regulation of automatic air conditioning, function | GF83.40-P-2004SX |
| Ventilation system, function | GF83.10-P-2000SX |