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Discussion Starter · #1 ·
Hello fellow Alfisti!

I finally took the decision to install an A/C to my 1.8 IE 75.
I have purchased all necessary items that are required (Heater box, compressor, a/c controls etc.) but I'm missing the engine compartment's wiring harness.

After studying the relevant electrical diagrams I found on the net, I understood more or less what needs to be done, but I still can't figure out a couple of things:

1) How does the ECU receive signal to increase the engine idle when a/c is on?
I guess there is a connector somewhere in the firewall that sends signal when the compressor engages. Does anyone have a picture with the location of this connector and the where these wires come from?

2) Is the a/c wiring harness routed along the right hand side inner fender, together with rest of the engine's wires?

3) How do the wires that connect to the heater box get to the engine bay? Is there a seperate hole on the firewall?

Any help/pictures will be greatly appreciated!!

Note: the car is an 1991 1.8 Alfa 75 with Motronic Fuel Injection.

Alexandros
 

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Luckily the A/C system isnt too complex on these cars so this shouldnt be too much of an undertaking.

1) The Motronic merely gets 12V on a pin on the ECU when the compressor is engaged. this can be fed from the spare pin left on the A/C relay as its a SPDT relay (or is supposed to be). Now im not sure what pin it is, youd think there should be a single connector ready for this somewhere

2)there is not any A/C harness as far as im aware. The heater gets its power from the fuse box and then travels to the center stack inside. The only thing outside the center stack for the A/C to work is the compressor in the engine bay, fed by the single wire on the A/C temperature switch. you really only need one wire, and rather a whole harness to pin 85 (coil) of the relay then to ground which runs the A/C compressor through a 10A fuse then to ground. Supply for the compressor itself can be found anywhere in the engine bay frankly...

3)on my 3.0 car, the compressor trigger wire gets to the engine bay via the lighting harness and not the ECU harness. if its possible, id just poke a tiny hole on the grommet and squeeze it through that.
 

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Discussion Starter · #3 ·
Thank you very much for the reply Brendan!

I searched a bit the forum and from what I understood it's either that pin 29 or pin 32 (or maybe both??) gets triggered with 12V when the A/C is turned on.
Is this correct?

Anyone knows where the connector that leads to these pins is located?

Also, does anyone know which way the idle is regulated when the signal is sent to the ECU? Is this done with the use of the ICV only or is it the timing that gets affected?

I'm asking because I'm not using the Motronic Ignition anymore as I have converted to Alfetta style electronic ignition.

Alexandros
 
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