Design and Function

Design and function

Air conditioning
See: Air conditioning Air Conditioning

Air distribution system
See: Air distribution system Air Distribution System

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 consist of a tubular coil through which the engine's coolant flows. The tube is fitted with flanges which give off heat to the passing air. The throttle valve in the distribution housing is set so that the blower can force a larger or smaller amount of the air flow through the heat exchanger. Here the air is heated before it is once again mixed with the remaining flow and distributed to the passenger compartment through several different outlets.
The heat exchanger is accessed from the right-hand side of the distribution housing.

PTC element (Positive Temperature Coefficient)




A diesel engine has optimal efficiency and therefore generates very little surplus heat. On some markets with a cold climate the vehicle uses a diesel engine with a PTC element as an extra heater.
Even four cylinder engines, in some cold markets, use a PTC element. The PTC element is also available as an option.
The PTC element heats the passenger compartment quicker at lower outdoor temperatures. This is essential as the coolant does not emit sufficient heat, especially during the initial minutes after the engine has been started.
The PTC element is placed in the climate unit after the heat exchanger. It is accessible from the front.
The air that flows past the hot PTC element, on its way into the passenger compartment, is heated directly.
Typical characteristics of a PTC element:
- fast heating directly after start
- high degree of efficiency
- lightweight, compact design
- cannot be overheated
- maintenance free.




The PTC element consists of small metal coated ceramic plates (1) sandwiched with radiator elements (2) of aluminium. These layers are held together in a frame (3) of a spring element. The aluminium element has the task of conducting current at the same time as it transfers heat to the air flow.
The maximum output of the PTC element is 1250W.




The PTC element has a positive thermal coefficient. This means that the resistance value is relatively small at low temperatures and increases with the rising temperature.
When the cold PTC element is voltage fed, the current is high during the initial stage and heats up the element. With a rising temperature the ceramic's resistance value also increases whereupon power consumption drops.
It takes approximate 20 seconds until the stabilization current is reached. The ceramic temperature is dependent on the heat output and the ambient temperature. With good thermal dissipation the temperature drops and with that the resistance. This results in an increase in power consumption and with that an increase in temperature.
If a small amount of heat is emitted to the surroundings, the temperature of the ceramic rises and with that the resistance. Through this cycle the heating element is regulated with its own power consumption. The result is an equilibrium between the supplied electrical energy and the emitted thermal energy.
The Climate control module (CCM) controls, via the Central electronic module (CEM), the function of the PTC element. For more information, see Design and Function, Climate control module (CCM) and Design and Function, Central electronic module (CEM).

Additional heater/Parking heater




The heater can act as a additional heater or as a parking heater depending on the configuration of the vehicle. Additional heaters are standard in vehicles with diesel engines on some markets with a cold climate. The heat produced by the diesel engine is not sufficient to obtain a pleasant passenger compartment temperature.
Through the combustion of gasoline or diesel the additional heater/parking heater produces heat. The heat is distributed by the engine's cooling system to the heat exchanger and onward out into the passenger compartment.
When the engine is running, the additional heater can supply extra heat into the passenger compartment if the engine is not capable of supplying sufficient heat. When the engine is not running, the parking heater can preheat the passenger compartment (and the engine). This function can be started immediately or by using a timer.
A number of conditions need to be met to start the additional heater. For information, see Design and Function, combustion preheater module (CPM).
The parking heater is controlled via the steering lever. Information is displayed on the Driver information module (DIM).
The additional heater/parking heater is located in the front, right-hand wheel housing up against the A-pillar and covered by the plastic wheel arch liner.




1. control unit with fan and Combustion preheater module (CPM)
2. burner unit
The heater is connected to:
- the engine cooling system
- the fuel tank
- The controller area network (CAN)
The additional heater/parking heater is also equipped with a coolant pump. A fuel pump is located on the rear axle behind the fuel tank. The fuel pump is connected, without filters, to a separately prepared tank connection.
For more information about the additional heater/parking heater, see Design and Function, Combustion preheater module (CPM).

Location of the components in the climate unit





Hint: Side view of the climate unit.