Engine cooling fan control

ENGINE COOLING FAN CONTROL

(3.0 V6 24v engine)

Two fans P2a and P2b ensure the necessary ventilation of the cooling air for the engine radiator and air conditioning system condenser.

N.B.: the two fans are in parallel, therefore they are operated together, always following the same logic.

The two fans are always supplied by battery voltage, through the line protected by wander fuse G254; they are operated by an earth command signal: this signal arrives directly (2nd speed) or through the additional resistances O22a and O22b (1st speed), fitted with a thermal safety fuse.

The delaying device Q42 controls the gradual engagement of the fans which are operated at two different speeds, also via two relays I99b and I100; the relays are located on the auxiliary bracket next to the fuse-box, as the delaying device is located in the engine compartment, RH side.

The delaying device works according to the following logic:

The "key-operated" voltage (line protected by fuse F17 of G1) supplies the coil and the electronic devices of the delaying device Q42 -pin 85, and relay I99; the coil of the delaying device Q42 is energised by an earth signal -pin P- which leads from the trinary pressure switch Q20: this causes the immediate sending of an earth signal - pin 30 - to energise relay I99 which sends the earth command to the two engine cooling fans P2a and P2b through the additional resistances O22a and O22b: 1st speed.

After appr. 12 seconds, if the signal from the trinary persists, the delaying device operates the second speed: in fact, the earth signal is cut off from pin 30 and a signal leaves pin 86, which energises I100 which sends the earth command directly to the two engine cooling fans P2a and P2b: 2nd speed. When the signal from the pressure switch ceases, the fans are disengaged.

The two fans are operated at the two different speeds also by the two-level thermal contact L33 which controls the temperature of the coolant in the engine radiator: when a first level is reached, relay I99 is energised which sends the earth command to the two engine cooling fans P2a and P2b via resistances O22a and O22b: 1st speed. Relay I100 is supplied by the line protected by fuse Q39 (30A).

If the second temperature level is reached, relay I100 is energised which sends the earth command directly to the two engine cooling fans P2a and P2b: 2nd speed.