Functional Description

Functional Description

The electromagnetic joint that operates the compressor Q11 is actuated by the corresponding relay Q22.

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

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

• the positive signal leading from the switch in Q68, before reaching relay Q22 it crosses the compressor cut out thermal contact Q12 (which cuts off the compressor if the engine is very hot) and the pressure switch Q20.
• The signal also crosses control unit Q21 which comes into operation in the following conditions:
• low outside temperature: (disengagement below 4°C and re-engagement above 6°C);
• low mixed air temperature (disengagement below 3.5°C and re-engagement above 5°C);
• the signal leading from the control unit Q67 is either 12 V or 0 V (earth), according to the following logic,

depending on the 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-, and therefore the compressor electromagnetic joint is not energised; conversely, as soon as the switch opens again the signal from pin 7 becomes 12 V, energising the joint;
• over 2000 rpm: the earth signal is timed and lasts only 8 seconds, then it becomes 12 V. and therefore the joint is energised, thereby engaging the compressor, if still required by the special button Q68.

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

When energised, relay Q22 operates the electromagnetic joint Q11 which turns on the compressor.