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Old 09-07-2009, 08:04 PM   #1
Ben
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Default A/C Control with Standalone on 99

Joe's Great A/C Thread leaves a lot of speculation, and the links to the NB diagrams are broken.

I'd like to reopen this topic and come to consensus.

Here is the A/C system wiring diagram for a 99


If I am reading correctly, it appears that I can jumper 1P to 1I and 1S. If I do so, it looks like the a/c fan and a/c comp clutch relay coils will take a ground path through the pressure switch, the a/c amplifier, the a/c dash pushbutton, and the fan switch, finally getting to a chassis ground behind the dash.

This may work fine. Or it may not. I don't know.

I was considering trying something else. Can/Should I use a couple transistors in this manner?


Bottom line is I want the a/c to function, and I don't want to use any I/O on the MS itself.

Comments, opinion, wild speculation all appreciated.
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Old 09-08-2009, 02:30 AM   #2
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You need to use at least one output to switch off the compressor when rpms are high.

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Old 09-08-2009, 09:28 AM   #3
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I considered and dismissed the thought. I don't have the I/O for it. My right pointer finger will work just as well.
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Old 09-11-2009, 05:47 PM   #4
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I spoke with Jerry of DIY Autotune fame earlier. He advised me to not simply jump grounds. Here's the skinny.
The ground provided by the a/c pushbutton is very high resistance. It is not sufficient to reliably trigger the relay coil grounds. He says that it can and will cause the a/c relay(s) to fail.

So don't just jump them. Use a transistor. This applies to all years.
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