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 the relay Q22 from the compressor cutout control unit Q67, and from the control switch Q68:

• the earth signal leads from relay Q69, which is energised with a signal leading from the compressor cutout switch Q68; this signal crosses the control knob Q4 which cuts it off when the actual knob is in the "OFF" position: in this condition, in fact, the compressor cannot be engaged. In addition, before reaching relay Q22 crosses the compressor cutout thermal contact Q12 - which disengages the compressor if the engine is very hot, and - from chassis no. .... - pressure switch Q20. In this version there is also an auxiliary relay Q32 which is energised by the earth signal leading from relay Q69 and controls relay Q21.
• the signal from the control unit Q67 is either 12 V or 0 V (earth), according to the following logic, in relation to engine rpm (information picked up directly from 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 compressor electromagnetic joint is not energised; vice versa as soon as the switch opens again, the signal from pin 7 becomes 12 V, energising the joint;
• above 2000 rpm: the earth signal is timed and lasts only for 8 seconds, then it becomes 12 V, therefore the joint is energised and engages the compressor, provided that the pushbutton Q68 has been pressed.

The control unit Q67 is connected, as mentioned previously, to the rev counter sensor L16 at pins 3 and 6, to switch H54 at pin 5; pin 2 is earthed, while pin 1 receives the "key- operated" supply via relay I35 and fuse F4 of the fusebox G1: the signal for engaging the compressor leaves pin 7 as described above.

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

This control signal - up to chassis no. .... - must not however be cut off by the minimum and maximum pressure switch (trinary) Q20 - located between relay Q22 and the compressor joint Q11 - which cuts in if the pressure of the cooling system is too high or too low.

Relay Q22 and fuse Q65 are to be found - up to chassis no. .... - in the set of fuses and relays Q41.