Quote:
Originally Posted by kglowacky
going thru the same process of getting my ac working. when I got my harness back from the rebuilder he left a wire on it saying AC. I called and asked why he left it on there because I said no to ac on the build. He said they made a mistake just ignore it. Now I am wondering if he didn't do me a favor by leaving it. My question is is this wire connect to 12v or a ground or does it connect to the compressor and the compressor tell the ECM to increase rpms to handle the extra load. or connect to a relay terminal. Assume it is pin#17.
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More than likely, he left you the a/c request line from/to pin #17 of the ECM. Most people wire the a/c request line together with the compressor wire (see above diagram by OP). The problem is that ECM is not controlling the compressor but rather the compressor request is controlling the ECM and telling it to increase idle due to the extra load. But, it really is too late at this point and you will feel dips in the idle speed.
On the other hand, if you let the ECM control the compressor, then the ECM anticipates the added load and compensates almost imperceptibly. And, the ECM can cut out the compressor as necessary such as during starting and full throttle, etc.
For ECM control of the compressor, ECM pin #43 must control the compressor. Pin #43 is a ground output and must only be used to control a relay.