Engine fan control

increase of pressure at the condenser (cut in at appr. 15 bar):

• it stops the compressor, de-energizing the electromagnetic joint, if the pressure reaches very high, thus dangerous, values (above appr. 28 bar), or very low values to ensure correct operating conditions (below appr. 2.45 bar);

minimum pressure switch (defroster) - Boxer and T.SPARK versions only: this disconnects the compressor when the pressure is too low (<1.7 bar) to prevent the danger of the evaporator "frosting". It also protects the compressor from sharp pressure falls, caused for example by leaks in the circuit.

compressor cutoff thermal contact: - TD version only: this cuts off the compressor if the engine temperature reaches dangerously high levels (it is a contact to be found on the thermostatic cup, which cuts in opening the circuit above 111°C).

full load switch - TD version only: this is a mechanical microswitch on the injection pump which, through the special compressor cutout control unit, cuts in to shut off the compressor temporarily when the accelerator pedal is completed depressed (full load).

compressor cutout control unit - TD version only: this momentarily cuts out the cooling system under particular circumstances in which the engine needs to be able to deliver the maximum power to the wheels, eliminating the absorption of power by the compressor (for example when overtaking, rapid accelerations, uphill driving, etc.).

The control unit activates the following operating logic, or rather two different logics at low and high rpms: below 2000 rpm as soon as the full load switch closes, the compressor electromagnetic joint is de-energised, and vice versa it is engaged as soon as the switch opens again; above 2000 rpm the supply is cut off only for 8 seconds, then it is restored.

Engine fan control

When the car is travelling at low speed the cooling action of the dynamic air on the condenser is reduced and it is necessary to turn on the two fans which cool the engine radiator and the actual condenser. This is done by the trinary pressure switch which cuts in preventing an increase of the pressure at the condenser (over 15.2 bar).

The engine fans are firstly turned on at first speed, then through a timer - not fitted on the T.SPARK version - they gradually pass to second speed avoiding sudden actuations and overloads at the relay contacts.

The delay device works according to the following logic:

• The first speed is turned on with a signal from the pressure switch on the cooling fluid circuit: after appr. 8-12 seconds, if this signal persists, the delaying device operates the second speed.
• When the signal from the pressure switch ceases, the second speed is turned off immediately and the delaying device operates the first speed for appr. 0.5 second more.

Fuses and relays:

There is a box (Q41) in the engine compartment which contains the relays and fuses associated with the air conditioning system:

• cooling fan delaying device (Q42);
• compressor electromagnetic joint relay (Q22);
• additional compressor relay (Q32); - Boxer versions only
• 1st fan speed relay (I99b);
• 2nd fan speed relay (I100); - Boxer versions only
• 7.5A wander fuse (Q65);
• 3A wander fuse (Q66) - Boxer versions only

There is also the relay unit supply wander fuse and the 30A conditioning fuses (Q39), located next to the branch terminal box (Boxer versions only).

N.B.: For T.SPARK and boxer versions from chassis no. 4065018, and from chassis no. ... for the TD version, box Q41 is no longer present, and the fuses and relays are located on the bracket next to the fusebox

For further details concerning this system, refer to Group 50 "CLIMATE CONTROL".