General description

GENERAL DESCRIPTION

Climate control of the car through heater unit is insufficient when the engine is cold, especially in the case of Diesel engines, which reach the proper temperature more slowly.

An additional heating system is therefore provided for these engines and is activated during the initial seconds of engine operation, until a certain temperature is reached.

The system consists of an additional heating device, located on the engine coolant delivery pipe that leads to the engine heating unit.

There are three glow plugs on this device (similar to those used for preheating the combustion chamber).

Glow plug operation is controlled by an ECU that pilots one, two or three plugs to provide a heating of 200 W, 400W or 600W.

This control logic depends on:

• the temperature reached by the engine coolant;
• the amount of available electrical power (the battery voltage is controlled)
• engine rpm (which must exceed a pre-established value)

The power supply of one, two or three glow plugs is piloted by two remote switches:

• level 1: activated by the first remote switch;
• level 2: activated by the second remote switch;
• level 3: activated by both remote switches.

There is also a third remote switch/safety switch that interrupts power supply to the glow plugs if their contact to earth is incorrect: the metal device containing the glow plugs is in fact connected to the engine earth by means of a special braid.

OPERATIONAL DESCRIPTION

The additional heater control unit N85 is protection-powered at pins 15 and U by the line protected by fuse F15 of the fuse box G1.

The engine rpm signal comes from the engine management control unit S11 and enters pin N of M75.

Pin TW is connected to the special temperature sensor L60 which detects the coolant temperature in the vicinity of the additional heater.

The remote switches I118 and I119 control connection of the three resistances O38.

Direct power reaches the battery through maxifuse G408, while the coils are energized by control unit N85, which controls only remote switch I118 to enable glow plug O38 A, only remote switch I119 to enable glow plugs O38 B and C, and both remote switches for all three glow plugs O38.

The safety remote switch I120 interrupts the power supply of the above-mentioned glow plugs if they are incorrectly earthed: the coil of I120 is connected on one side to earth and on the other side to the metal frame of the device containing the glow plugs: the device is connected to earth G53a through a special earthing braid: if this connection is interrupted, remote switch I120 is energized and immediately blocks the distribution of electricity to the glow plugs.