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Old 08-03-2022, 06:44 PM
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Default Where does the AC Fast Idle Solenoid wire tie in on a 68?

My 68 has a factory AC system, but is missing the fast idle solenoid. I have a couple of them in my pile of stuff I acquired over the years, so I would like to add it back into the system. The question I have is where does this tie into the A/C system. I found this wire harness for a Chevelle / Camaro fast idle solenoid. This looks like the compressor wire plugs into this harness and then the other dual clip goes to the compressor and single wire to the solenoid. Does that sound correct?

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Old 08-03-2022, 07:37 PM
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What you're calling a fast idle solenoid doesn't tie into the A/C. It's an anti diesel solenoid. It closes the throttle when the key is turned off. The wire leading to the solenoid is hot all the time when the ign switch is turned on.

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Old 08-03-2022, 09:04 PM
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Quote:
Originally Posted by necdb3 View Post
What you're calling a fast idle solenoid doesn't tie into the A/C. It's an anti diesel solenoid. It closes the throttle when the key is turned off. The wire leading to the solenoid is hot all the time when the ign switch is turned on.
I see this as a solenoid that serves two totally different purposes, yet is the same solenoid. For manual trans cars, it serves to lower the rpm when the ignition switch is turned off so it doesn't diesel. On AC cars (which are normally auto trans cars in 68), it ups the rpm when the AC is on, hence the confusion. I am more than happy to be corrected and will learn something here.

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Old 08-04-2022, 12:11 AM
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I could be wrong, but if you look at the AC wiring schematics for 68 they don't show the solenoid anywhere.

I suppose there could be a tie in to the ignition/engine harness that is not shown? Would have to tie into the AC controls on the dash, but I've never seen it.

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Old 08-04-2022, 12:52 AM
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All 68 Pontiacs, OHC and V8, manual and automatic, A/C and heater equipped, had the anti-dieseling solenoid. It has nothing to do with the A/C and as mentioned above, is energized whenever the key is 'ON'. To set the idle you turn the armature shaft of the solenoid to the correct idle speed.

Powered by a single black with white tracer wire

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Old 08-04-2022, 08:48 AM
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Gents, thank you for correcting me. I did go back into the manuals and the wiring as you outlined is verified by the 68 service manual. I couldn't find any alternate wiring with a tie to the A/C system. My confusion comes from several other strings in the heating / cooling section of this forum referencing using this solenoid for increasing idle speed only when the A/C was running. Since my car doesn't diesel now without the solenoid, I suppose that could be a use for it if the wiring is instead routed to become hot only when the A/C kicks in. Anyway, thanks for the help.

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Old 08-04-2022, 11:47 AM
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Quote:
Originally Posted by OG68 View Post
All 68 Pontiacs, OHC and V8, manual and automatic, A/C and heater equipped, had the anti-dieseling solenoid. It has nothing to do with the A/C and as mentioned above, is energized whenever the key is 'ON'. To set the idle you turn the armature shaft of the solenoid to the correct idle speed.

Powered by a single black with white tracer wire
I believe that same set up (including the same PN solenoid) was used from 68 thru 72.

IIRC PN 1997405, Perhaps they had supersessions, Just looked it up 1114423

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Old 08-04-2022, 11:52 AM
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I think so too. Just didn't take the time to verify other years.

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Old 08-04-2022, 12:44 PM
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Like OG68 mentioned, black with white tracer… should be in the bundle heading towards your alternator along with the temp sender wire (if I’m not mistaken).

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Old 08-04-2022, 07:11 PM
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And the procedure for solenoid idle speed setup is printed on the black core support label.

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