A/C on input?

E28 technical advice asked and given! Troubleshooting, modifications and more.
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roadstar
Posts: 46
Joined: Aug 17, 2012 2:13 PM

A/C on input?

Post by roadstar »

Hi!

I am restoring my engine harness (535i 1987) and am wondering about the loose wire/connector attached to the power feed and injection control wires to the ignition coil. I understand this is supposed to be attached to the a/c compressor clutch. I have no a/c in my car so I guess that is why it´s hanging loose.

The question is what kind of signal is passed from this connection to the ecu? Ground or power?

I got curious about this since my car has always had low idle and there is not one thing on this forum that I have not checked. Since this signal is, to my knowledge, supposed to raise idle when a/c is activated, it might push my idle up a notch?

Henrik.
adam_poll
Posts: 206
Joined: Jul 23, 2014 8:19 PM
Location: Kitchener, Ontario, Canada

Re: A/C on input?

Post by adam_poll »

Looking through the ETM it looks like this signal to the ECU goes high when the A/C clutch is engaged, it is actually just tapped right off the clutch signal itself. So basically you should put 12V on that to simulate the A/C being on.

I've sent you PM with a link to download the ETM if you don't already have it. On page 36 for the 87 E28 it shows the input going to Pin 29 of the ECU and on page 113 it shows a Blue/Black wire from the compressor clutch to the ECU, if you trace that back through it is 12V supplied by fuse 14.
roadstar
Posts: 46
Joined: Aug 17, 2012 2:13 PM

Re: A/C on input?

Post by roadstar »

Big thanks for the info! I actually have the Bentley-manual but obviously not the skills to read electrical symbols. :?
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