"MAX-DEF" Function

"MAX-DEF" Function

With the distribution knob turned completely in a clockwise direction the "MAX DEF" rapid demisting function is activated by a special microswitch. This function involves:

• maximum air flow rate
• mixture with maximum heat available
• recirculation switched off, whatever position the button (5) is in
• compressor enabled, whatever position the button (4) is in
• signal requesting engagement of heated rear windscreen : this engagement is managed by the integrated services control unit (see Group 55)

Compressor engagement

When the button shown in the diagram is pressed this enables the OPERATION OF THE COMPRESSOR (air refrigeration circuit); if the button is released, the operation ceases.

The effective engagement of the compressor, however, depends on the following conditions:

• outside temperature below 5°C: (switches off below 4°C and switches on again above 6°C)
• temperature detected by the frost sensor: (switches off below 3.5°C and switches on again above 5°C)

It should be rememebered that the compressor can also be switched off through the intervention of the four stage pressure switch or the engine control unit. This logic dependson the different engine management control units, as detailed below:

CONNECTION WITH THE ENGINE CONTROL UNIT

The electronic control unit for the climate control system sends a command signal to the engine control unit giving the go ahead required for engaging the compressor.

There are two different types of connection according tothe type of engine control unit

A: 1242 - 1581 - 1998 - 1910 JTD engines

B: 1910 TD 75 engine (Soft)

NOTE For the 1747 version, refer to the details in the previous edition (print no.506.670/01).

NOTE For the 1910 TD 75 version, which does not have an engine control unit, the go ahead for operating the compressor is given by a special thermal switch and by the EGR control unit, as well as the four stage pressure switch.