Functional Description

Functional Description

The electromagnetic joint which operates the compressor Q11 is operated by the corresponding relay Q22.

Relay Q22 is supplied directly by the battery, via fuse Q65.

The two energising signals (12 V and earth) reach relay Q22 from the compressor disengagement control unit Q67, and from the control switch Q68:

• the positive signal leading from the switch in Q68, before reaching relay Q22 crosses the compressor cut out thermal contact Q12 (which turns off the compressor if the engine is very hot), the pressure switch Q20 and the thermostat Q71 which cut off the signal respectively for high or low pressures and low temperatures;
• the signal leading from the control unit Q67 is either 12 V or 0 V (earth), according to the following logic, depending on engine rpm (information picked up directly by the rev counter sensor L16:

• up to 2000 rpm: when the full load switch H54 closes, an earth signal leaves the control unit -pin 7-, therefore the electromagnetic joint of the compressor is not energised; vice versa as soon as the switch opens again, the signal from pin 7 becomes 12 V, energising the joint;
• over 2000rpm: the earth signal is timed and lasts only 8 seconds, then it becomes 12 V, therefore the joint is energised, thereby engaging the compressor, if this is still requested through the special button Q68.

The control unit Q67 is connected, as mentioned previously, with the rev counter sensor L16 at pin 3 and 6, to switch H54 at pin 5; pin 2 is at earth, while pin 1 receives the "key-operated" supply via relay I35 and fuse F4 of box G1 (box "A") or only by fuse F14 still in G1 (box "C"): the compressor engagement signal leads from pin 7 as described above.

When it is energised, relay Q22 operates the electromagnetic joint Q11 which engages the compressor.