Functional Description

Functional Description

Two coolant fans P2a and P2b provide the required ventilation for cooling the engine radiator and air conditioning system condenser.

The injection control unit S11 controls the fan for cooling the engine coolant fluid and the conditioning system coolant fluid.

This way, the thermal contact usually installed on the radio is dispensed with. The two speeds of the fan are controlled on the basis of the engine temperature, detected by the control unit through the special sensor: a "low" signal (earth) leaves pin 23 of connector B which controls the first speed relay I99, and a "low" (earth) signal leaves pin 45 of connector C which controls the second speed relay I100.

The "key-operated" voltage (line of fuse F14 of control unit G1) supplies the coils of relays I99, I100 and I121.

The first speed signal energizes remote switch I99 which powers – with the G254b maxifuse line – electric fan P2a: the fan rotates at low speed because it receives a "damped" earth from fan P2b; through the non-energized switch I121, fan P2b also rotates at a low speed.

The second speed signal energizes remote switch I100 which powers – with the G254 maxifuse line of G56 – the electric fan P2b at maximum speed; simultaneously the same signal energizes the switch I121 which sends an earth to fan P2a. This fan also rotates at maximum speed.

Pressure switch Q20 also sends special signals to the control unit S11 for engaging the fans if the pressure of the coolant fluid in the circuit exceeds determine ratings:

• over approx. 15 bar the signal is sent to pin 3 of connector B for engaging the 1st speed;
• over approx. 20 bar to pin 15 of connector D for the 2nd speed.