Design
Design
Air conditioning
See: Air conditioning Air Conditioning
Air distribution system
See: Air distribution system Air Distribution System
Blower fan
The blower fan is a permanent magnet type fan. The fan contains no brushes, which means that there is less wear. The fan wheel is of the radial type with a guide vane rim on the outer edge of the wheel. The fan wheel is balanced using steel clips.
Filter
There are two types of filter.
- Particle filter
- Multi-filter.
The particle filter is standard.
The multi-filter is a CNG filter. The multi-filter is only available for vehicles with electronic climate control (ECC) and then in combination with the air quality sensor (AQS).
Heat exchanger
In order to heat the air in the passenger compartment, the heating system uses the heat that is generated by the engine. The heat exchanger is connected to the cooling system for the engine. The outlet connection for the heat exchanger is located directly on the engine at the point where the pressure and temperature of the coolant are highest. The coolant flows through the cooling ducts for the engine block and on into the heat exchanger. The return flow is connected to the return pipe on the suction side of the water pump. The heat exchanger comprises a pipe loop through which the engine coolant flows. The pipe has flanges that provide heat to the airflow. The shutters in the distribution housing are set so that the blower fan can direct a larger or smaller portion of the airflow through the heat exchanger. The air is heated there before being mixed again with the remaining flow and distributed to the passenger compartment through a number of different vents.
PTC element (Positive Temperature Coefficient)
A diesel engine has optimal efficiency and therefore emits very little surplus heat. In cold climates, vehicles with diesel engines therefore use a PTC element as an extra heater.
The PTC element means that the passenger compartment can be heated up quickly in low ambient temperatures. This is necessary as the coolant does not emit sufficient heat, particularly during the first minutes after starting the engine.
The PTC element is located in the climate control unit after the heat exchanger. The air that flows past the hot PTC element on its way into the passenger compartment is heated directly.
Typical properties for a PTC element are:
- rapid heating immediately after starting
- high level of efficiency
- lightweight, compact design
- cannot overheat
- maintenance free.
The PTC element comprises small, metal-coated ceramic plates (1) interspersed with radiator elements (2) made of aluminum. These layers are held together in a frame (3) of spring elements. The task of the aluminum elements is to conduct the current at the same time as transferring heat to the airflow.
The maximum output of the PTC element is 1000 W.
The PTC element has a positive heating coefficient. This means that the resistance value is relatively low at low temperatures and increases as the temperature rises.
When the cold PTC element is supplied with power, the current is high in the initial stage and heats up the element. As the temperature rises, the resistance value of the ceramic also rises. As a result, the power consumption falls.
It takes approximately 20 seconds until the stabilization current is reached. The ceramic temperature is dependent on the heat given off and the ambient temperature. In the event of good heat transfer, the temperature falls, as does the resistance. As a consequence, the power consumption and the temperature both rise.
If little heat is given off, the temperature of the ceramic rises, as does the resistance. With this cycle, the heating element regulates its own power consumption. The result is an even balance between electrical energy supplied and heat energy given off.
The climate control module (CCM) checks the function of the PTC element via the central electronic module (CEM). For further information, see Design and Function, climate control module (CCM), and Design and Function, central electronic module (CEM).
Additional heater/Parking heater
The Additional heater/Parking heater is located by the firewall on the right-hand side of the engine compartment. The heater consists of:
- the heater unit
- the combustion preheater module (CPM)
- the exhaust system with muffler
- the air intake.
The heater is connected to:
- the engine cooling system
- the fuel tank
- the Control area network (CAN).
The heater is checked by CAN signals. The parking heater also has a water pump. Both versions have a fuel pump (FP) located on the rear axle near the fuel tank for the vehicle.
The turn signal lamp stalk is used to control the heater. The information appears in the driver information module (DIM).
For further information about the additional heater/parking heater, see Design and Function, combustion preheater module (CPM).
Location of the components in the climate control system
Hint: The illustration of the climate control system is drawn from the side.
1. Air intake
2. Blower fan
3. Filter
4. Evaporator
5. Heat exchanger
6. PTC element
7. Temperature shutter
8. Air duct to floor rear
9. Air duct to floor front
10. Air duct to dashboard vents
11. Defroster.