Operating logic

The heating inside the vehicle via the heater unit is insufficient, with the engine cold, especially in the case of diesel engines which reach operating temperature more slowly.
An additional heating system is offered for these engines which is activated when the engine is first running until a certain temperature is reached.
The system consists of an additional heating device, located on the engine coolant supply pipe to the heater unit.
This device contains three spark plugs which are very similar to those used for pre-heating the combustion chamber.

Location of car interior coolant heater plugs

The additional heater containing the three heater plugs is located on the coolant supply pipe to the heater unit.
The coolant temperature sensor is located on the same pipe, immediately upstream towards the engine thermostat.
The three relays are connected by the diesel filter, on a special bracket fixed to the engine compartment bulkhead.
The system control unit is located under the dashboard, behind the glove compartment.

Operating logic

The operation of the heater plugs is controlled by an electronic control unit which operates one, two or three heater plugs thereby giving a supply 200W, 400W or 600W

This control logic depends on:
- the temperature of the coolant leaving the engine;
- the power level available;
- the engine speed.

The first information is supplied by a special temperature sensor located on the supply pipe towards the heater; the control logic deactivates the heater plugs when the temperature of the coolant coming from the engine exceeds 70 °C.
The control unit also takes into account the parameter of the temperature of the air in the engine compartment; it is not measured by a special sensor, but is assumed to be the same as the temperature of the coolant during starting; the switching off figure decreases from 70 °C to 65 °C if the temperature of the air is assumed to be greater.