Functional Description

Functional Description

• up to chassis no. 4065017

The electromagnetic joint which operates the compressor Q11 is controlled by relays Q22 and Q32, to be found in the set of relays and fuses Q41.

Relays Q22 and Q32, have the coil supplied from the ignition switch (line protected by fuse F17 of G1); their power line is supplied by battery voltage through fuse Q65 (7.5A), also located in group Q41, as well as through floating fuse Q39 (30A) which protects the entire system.

Relay Q22 is energized and consequently supplies 12V to the electromagnetic joint Q11, according to the following logic:

BOXER Version 1.6 (MOTRONIC MP3.1):

• Relay Q32 is energized by a signal leading from Q69, which is in turn energized with a signal leading from the compressor operating switch Q68; this signal crosses the control knob Q4 which interrupts it when the knob itself is in the "OFF" position. In this condition, the compressor cannot be turned on. It should be remembered that the same signal controls the first speed of the fan contemporaneously ("Fan and Recirculation Control").
• the same control signal is also sent to the other relay Q22: this signal crosses the minimum pressure switch (antifrost) Q9 and the minimum and maximum pressure switch (trinary) Q20 which intervene if the pressure in the cooling system is too high or too low: in this case the control signal does not reach Q22 which operates the compressor.
• relay Q32 sends a signal to the Motronic control unit MP3.1 (pin 29) which informs this system about the "request" to turn on the compressor.
• the other signal sent to the control unit (pin 32 of the Motronic MP3.1 control unit) is the one which supplies joint Q11, and thereby informs that the compressor has actually been turned on.

BOXER Version 1.3 and BOXER 1.6 (ROCHESTER):

• relay Q32 is energized by a signal leading from relay Q69, which is in turn energized with a signal from the compressor operating switch Q68; this signal crosses the control knob Q4 which interrupts it when the knob is at the "OFF" position: indeed in this condition the compressor cannot be turned on. It should be remembered that the same signal controls the first speed of the fan contemporaneously ("Fan and Recirculation Control").
• relay Q32 consequently sends a signal to the IAW control unit S40, to pin 8 (IAW) or pin A8 (Rochester), which crosses the minimum pressure switch (antifrost) Q9 and the minimum and maximum pressure switch (trinary) Q20 which intervene if the pressure in the cooling system is too high or too low: in this case the signal does not reach the control unit S40 which does not command the turning on of the compressor
• the control unit "refers" the command signal - pin 24 (IAW) or pin A15 (Rochester) of S40 - to relay Q22 which is energized and supplies joint Q11 which turns on the compressor, but only when the internal logic has ascertained determine conditions (for example the compressor does not turn on in the event of the engine requiring full power, etc...)

BOXER Version 1.7 16v:

• relay Q32 is energized by a signal leading from relay Q69, which is in turn energized with a signal leading from the compressor switch Q68; This signal crosses the control knob Q4 which interrupts it when the knob itself is in the "OFF" position. In fact in this condition, the compressor cannot be turned on. It should be remembered that the same signal controls the first speed of the fan contemporaneously ("Fan and Recirculation Control").